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IRRIGATION 


IRRIGATION: 

ITS    PRINCIPLES    AND    PRACTICE 

AS  A  BRANCH  OF  ENGINEERING 


BY 

SIR   HANBURY    BROWN,    K.C.M.G. 

Member  of  the  Institution  of  Civil  Engineers 
(late  Royal  Engineers) 


THIRD    EDITION    REVISED 


LONDON 

CONSTABLE    &    COMPANY    LTD 
10  ORANGE  STREET   LEICESTER  SQJJARE   WC 
1920 

D.  VAN  NOSTRAttD  COMPANT 

N.KW 


Printed  in  Great  Britain. 


PREFACE  TO  THE  THIRD  EDITION. 


THE  primary  object  of  this  book,  as  stated  in  the  original 
Preface  which  follows,  is  to  set  forth  "  guiding  principles." 
These  do  not  change  with  lapse  of  time.  But  some  of  the  works, 
or  matters  connected  with  them,  which,  in  previous  editions, 
have  been  made  use  of  as  illustrations  of  the  application  of 
those  principles,  have  advanced  a  stage  in  their  growth  or 
development  since  they  were  so  used.  Still,  that  does  not  alter 
their  value  as  illustrations  in  their  previously  existing  states. 
Consequently,  as  this  book  deals  with  principles,  and  only  with 
works  so  far  as  they  illustrate  those  principles,  it  has  been 
decided  that  nothing  would  be  gained  by  making  alterations 
in  the  text  because  the  works,  projects  or  estimates,  cited  as 
illustrations,  are  not  now  as  they  were  at  the  time  the  previous 
edition  was  published.  But  to  avoid  conveying  any  wrong 
impression  of  actual  facts  by  adopting  this  course,  Appendix  IV. 
is  added  to  this  third  edition  with  the  object  of  drawing  atten- 
tion to  any  changes  that  have  taken  place,  whenever  it  seems 
desirable  to  do  so. 


4341 05 


PREFACE  TO  THE  FIRST  EDITION. 


IRRIGATION  is  a  subject  which  covers  much  ground,  and 
cannot  be  confined  within  the  narrow  boundaries  of  a  single 
volume.  But  the  principles  on  which  Irrigation  Engineering 
is  based  can  be  collected  in  small  compass,  and  be  illustrated 
by  examples  of  actual  practice  to  the  extent  that  space  allows. 
What,  therefore,  this  work  attempts  to  do  is  to  set  forth  the 
guiding  principles  that  should  govern  the  practice  of  irrigation, 
and  to  furnish  illustrations  of  their  application  in  existing  canal 
systems.  The  majority  of  the  illustrations  have  been  selected 
from  the  wealth  of  material  that  the  irrigation  experience  ol 
India  and  Egypt  supplies,  for  the  following  reasons.  In  the 
first  place,  I  have  been  personally  connected  with  irrigation  in 
both  countries,  and  can  therefore  handle  the  facts,  relating  to 
them,  as  one  having  authority  on  the  subject,  and  "  not  as  the 
scribes,"  whose  methods  I  might  be  imitating  were  I  to  draw 
my  illustrations  from  the  records  of  other  countries.  In  the 
second  place,  it  is  India  that  furnishes  examples  of  irrigation 
on  the  largest  scale,  and  that  has  been  the  school  in  which  all 
British  irrigation  engineers,  previously  to  England's  occupa- 
tion of  Egypt,  have  undergone  their  training.  Moreover,  the 
excellent  standard  work  on  the  subject,  "  The  Irrigation  Works 
of  India,"  by  R.  B.  Buckley,  C.S.I.,  provides  in  a  convenie  t 
form  more  than  enough  material  for  copious  illustrations,  and  I 
have  made  much  use  of  it,  with  Mr.  Buckley's  kind  permission. 
But  it  will  be  found  that  Egypt  has  been  the  favourite  source 
of  my  borrowing.  There  are  two  good  (so  it  appears  to  me) 
reasons  for  this.  The  first  is  that  I  am  intimately  acquainted 
with  Egypt  as  an  irrigating  country.  The  second  is  that  Egypt 
is  par  excellence  the  country  of  irrigation,  as  it  is  wholly  depen- 
dent for  its  existence  on  its  mother,  the  Nile,  from  which  it  has 
never  been  weaned. 


viii  PREFACE. 

Engineers  entrusted  with  the  execution  of  important  works, 
such  as,  for  instance,  high  reservoir  dams,  would  naturally  not 
be  content  with  what  they  might  find  on  the  subject  in  a  book 
treating  of  irrigation  generally,  but  would  apply  themselves  to 
a  study  of  some  work  dealing  exclusively  with  the  special 
subject  of  Dams.  And  so  also  with  other  matters  which 
require  ample  space  for  adequate  description.  Concerning 
such  this  work  attempts  no  exhaustive  treatment,  as  being 
beyond  the  compass  of  its  embrace. 

I  am  much  indebted  to  Mr.  R.  B.  Buckley,  C.S.I.,  for  valuable 
suggestions  and  much  assistance  in  obtaining  and  shaping  the 
subject-matter  of  this  book.  I  am  also  under  obligations  to 
Mr.  W.  B.  Gordon,  Director  of  Irrigation,  Cape  Colony,  and  to 
Mr.  W.  L.  Strange,  Director  of  Irrigation,  Transvaal,  for 
sending  me  information  about  their  charges.  The  develop- 
ment of  irrigation  schemes  in  South  Africa  is,  however,  not 
sufficiently  advanced  for  illustrations  to  be  obtained  from  the 
reports  sent  me.  To  Mrs.  A.  T.  Kemble  my  grateful  acknow- 
ledgments are  due  for  her  kind  assistance  in  the  compilation 
of  the  Index ;  and  to  Lady  Brown,  more  than  to  any  beside, 
for  relieving  me  of  all  the  labour  of  preparing  this  work  for 
publication  other  than  that  of  authorship  only. 

Among  the  works  consulted  in  the  preparation  of  this  book, 
the  following  are  perhaps  those  from  which  I  have  borrowed 
most  :  "  The  Irrigation  Works  of  India,"  by  Buckley  ; 
"  Egyptian  Irrigation,"  by  Willcocks ;  "  Manual  of  Irriga- 
tion Engineering,"  by  Wilson  ;  "  Irrigation  du  Midi  de 
1'Espagne,"  by  Aymard  ;  Transactions,  American  Society  of 
Civil  Engineers,  International  Engineering  Congress,  1904, 
"  Irrigation "  ;  Report  by  Sir  William  Garstin,  G.C.M.G., 
upon  the  Basin  of  the  Upper  Nile ;  "  Design  and  Construc- 
tion of  Masonry  Dams,"  by  Wegmann  ;  "The  Improvement 
of  Rivers,"  by  Thomas  and  Watt  ;  Proceedings  of  the 
Institution  of  Civil  Engineers. 


TABLE    OF    CONTENTS. 


CHAPTER   I. 

IRRIGATION   AND   ITS   EFFECTS.  PAGE 

Irrigation  makes  good  Deficiencies  of  Rainfall  in  India-  -America — 
Egypt — Mesopotamia — Results  in  Egypt,  India,  United  States  of 
America,  France,  Italy  and  Spain i 

CHAPTER   II. 

BASIN    IRRIGATION. 

Earliest  Form — Natural  Inundations — Evolution  of  a  Basin  System 
— Programme  of  Filling  and  Emptying  Basins— Dimensions  of 
Basin  Banks — Inundation  Canals  of  India — System  in  South 
Africa 12 

CHAPTER   III. 

PERENNIAL    IRRIGATION    AND    WATER    "DUTY." 

Perennial  System  of  Irrigation — Preparation  of  Project — "  Duty  "  01 

Water 28 

CHAPTER   IV. 

SOURCES    OF   SUPPLY. 

Sources  Enumerated— Wells— Rivers— Lakes— Artificial  Reservoirs 
— Prevention  of  Loss  by  Evaporation  and  Absorption — Control 
of  Natural  Lakes — Storage  a  Necessity  in  Egypt,  India,  America, 
South  Africa — Reservoir  Sites — Diversion  of  Rainfall  from  one 
Catchment  to  another — Indian  Tank  System  .  •  .  •  43 

CHAPTER  V. 

DAMS   AND    RESERVOIRS. 

Necessity  of  Storage  Reservoirs— Rainfall  and  Flow-off— Waste  Weir 
Capacity — Reservoir  Capacity — Dams  Classified  and  Discussed 
— Earthen  Dams — American  "  Loose-stone  "  and  "  Rock-fill " 
Dams — Pressure  in  Masonry  Dams — Submergible,  Insubmergible 
and  Pierced  Masonry  Dams — Reinold's  Gates  .  .  .  63 


x  TABLE   OF  CONTENTS. 

CHAPTER   VI. 

MEANS    OF    DRAWING    ON    THE    SUPPLY.  PAGE 

Lifting  Machines -River  Regulators— Anicuts— Barrages— French 
Types— Site  of  Work— Different  Types  of  River  Regulators 
Described  and  Discussed — Pumping  Stations  ....  104 

CHAPTER   VII. 

METHODS    OF    CONSTRUCTION. 

Materials  Used— Method  of  Enclosing  Area  and  Pumping— Well 
Sinking — Cement  Grouting — Iron  Syphons  Floated  into  Place 
and  Sunk 141 

CHAPTER  VIII. 

MEANS    OF    DISTRIBUTION. 

Channels    of    a    Canal    System    Classified    and    Discussed — Silt — 

Irrigation  Canals — Drains 171 

CHAPTER   IX. 

MASONRY   WORKS   ON    IRRIGATION   CANALS. 

Works  Classified  —  Head  Sluices  —  Regulators — Escapes  —  Falls  — 
Fayum  "Nasbahs" — Regulating  Apparatus — Aqueducts,  Super- 
passages,  Level  Crossings  and  Syphons 190 

CHAPTER   X. 

METHODS     OF    DISTRIBUTION     OF    WATER,    ASSESSMENT    OF    RATES,    AND 

ADMINISTRATION. 

Distribution  at  the  Head  of  the  Canal  System — Method  of  Assess- 
ment— Rotation  System  as  Applied  in  Different  Countries — 
Custom  of  "  Priorities,"  United  States  of  America — Water  Rates 
— Administration  by  Government,  Association  and  Syndicate — 
Advantage  of  State  Control  .  .  .  .  .  .  .212 

CHAPTER   XL 

FLOOD    BANKS    AND    RIVER   TRAINING. 

Effect  of  Flood  Banks — Nile  Banks— Breaches,  how  caused — Neces- 
sary Precautions — Protective  Works — Training  Works  .  .  237 

CHAPTER   XII. 

AGRICULTURAL   OPERATIONS   AND   RECLAMATION   WORKS. 

Knowledge  of  Agricultural  Needs  Necessary — Over- watering— Re- 
clamation of  Salt  Lands — Pumping  Stations  for  Drainage  and 
Reclamation  .«•,,,.,.,.  250 


TABLE   OF   CONTENTS.  xi 

CHAPTER  XIII. 

NAVIGATION.  PAGE 

Conflicting  Opinion  on  Subject  of  Combining  Irrigation  and  Naviga- 
tion— Lock  Sites — Lock  Chambers,  Gates  and  Sluices — Cracks 
in  Locks 258 


APPENDIX   I. 

WEIGHTS    AND    MEASURES  .  267 

APPENDIX   11. 

FORMULAS    AND    DISCHARGE    MEASUREMENTS 369 

APPENDIX     III. 

BOOKS  OF   REFERENCE 378 

APPENDIX  IV. 

NOTES  .  ,  *  .      282 


LIST    OF    PHOTOGRAPHIC 
ILLUSTRATIONS. 

Facing  page 
PLATE         I.    ASSUAN  DAM 97 

II.  WATER-LIFTING  WHEEL,  EGYPT          •        .        ,        .     105 

III.  WATER-LIFTING  WHEEL,  SPAIN 106 

IV.  DAM  ON  THE  RIVER  GENIL,  SPAIN     .        .        .        .109 
V.  RIVFR  SPUR,  SPAIN       ...               ...    no 

VI.  THE  DELTA  BARRAGE,  EGYPT 128 

VII.  DELTA  BARRAGE,  WEST  WEIR  UNDER  CONSTRUCTION  160 

VIII.  KOSHESHAH  ESCAPE 195 

IX.  MEX  PUMPS  UNDER  ERECTION     ,        ,        „        ,        ,  256 


LIST    OF    FIGURES. 


CHAPTER   II. 

PAGE 

FIG.    i.    DIAGRAM  OF  A  NATURAL  INUNDATION  .       •       •  14 

2.  DIAGRAM  OF  INUNDATED  BASINS  .        .                •        •        •  14 

3.  SKETCH  MAP  OF  IMPERFECT  BASIN  SYSTEM       .        .        •  15 

4.  SKETCH  MAP  OF  IMPROVED  BASIN  SYSTEM         .        .        .  17 

5.  DIAGRAM  OF  FLOOD  CANAL ,        .  20 

CHAPTER  IV. 

6.  MAP.    THE  NILE  ABOVE  KHARTOUM           .        «       •       .  53 

CHAPTER  V. 

7.  CROTON  DAM,  EARTHEN  LENGTH        ,        .       •       .       •  76 

8.  FOY  SAGAR  TANK  DAM          .                77 

9.  KAIR  TANK  DAM 78 

10.  CASTLEWOOD  RESERVOIR  DAM 80 

11.  BETWA  DAM 82 

12.  LA  GRANGE  DAM 83 

13.  VYRNWY  DAM 84 

14.  CROTON  DAM,  SUBMERGIBLE  LENGTH         ....  85 

15.  HENARES  WEIR 85 

16.  NIRA  DAM 86 

17.  FURENS  DAM  ..........  87 

18.  PERIYAR  DAM 88 

19.  MARIKANAVE  DAM          ....                 ...  89 

20.  CROTON  DAM,  INSUBMERGIBLE  LENGTH      «...  90 

21.  ZOLA  DAM •        •  93 

22.  BEAR  VALLEY  DAM 93 

23  AND  24.    SPANISH  UNDER-SLUICES 94 

25.  BHATGARH  DAM 95 

26.  ASSUAN  DAM  .        • •        •  97 

27.  REINOLD'S  GATE  .«•••«.*.  101 


Xiv  LIST  OF   FIGURES. 

CHAPTER   VI. 

PAGE 

FIG.  28.  DIAGRAM  OF  PERENNIAL  CANAL  ......  in 

29.  NARORA  WEIR,  ORIGINAL 115 

30.  NARORA  WEIR,  STRENGTHENED  ......  115 

31.  NARORA  WEIR,  OBSERVATION  PIPES 118 

32.  NARORA  WEIR,  PRESSURE  DIAGRAM 120 

33.  CHENAB  WTEIR 122 

34.  DELTA  BARRAGE  WEIR         .......  122 

35  SONE  WEIR  SECTION 123 

36.  SONE  WEIR  CREST  SHUTTERS 123 

37.  STONEY'S  GATES 127 

38.  THE  DELTA  BARRAGE  CHANNELS         .        .        .        •  128 

39.  DELTA  BARRAGE  SECTION 129 

40.  DIAGRAM  OF  WATER  LEVELS,  DELTA  BARRAGE        •        .  132 

41.  ZIFTA  BARRAGE     .        .        .        .        .        .               ,  133 

CHAPTER  VII. 

42.  METHOD  OF  CLOSING  SPRINGS  BY  VERTICAL  PIPES  .        .  148 

43.  METHOD  OF  CLOSING  SPRINGS  BY  HORIZONTAL  PIPES       .  148 

44.  CAST-IRON  PILES  .........  151 

45.  GROUTING  APPARATUS  FOR  PILES        .        .        .        •        .  152 

46.  WELL  INTERVALS,  SHUBRA  .        ..••••  156 

47.  APPARATUS  FOR  GROUTING  BLOCKS             •        •        .  158 

48.  GROUTING  METHOD  FOR  FOUNDATIONS        •        •        •        .  162 

49.  GROUTED  END  WALL  OF  LOCK   ..,•».  162 

50.  GROUTING  BORES  IN  DELTA  BARRAGE        •        •        •       .  165 

51.  END  OF  PIPE  SYPHON  ....••».  169 

CHAPTER  VIII. 

5«.  SECTIONS  OF  MAIN  CANALS.        ,       .       .       .       ,       t  179 

53.  DISTRIBUTARY  CROSS-SECTION      ••••••  182 

CHAPTER  IX. 

54.  TREBENI  CANAL  HEAD-SLUICE     ••••••  igi 

55.  KOSHESHAH  ESCAPE      .        ••••••.  194 

56.  FALL  WITH  CUSHION     ...•••«.  196 

57.  NOTCH  FALL .       .       .  196 

58.  FORM  OF  NOTCH  .........  198 

59.  HORIZONTAL  CLOSING  PLANK      •••••.  201 


LIST   OF   FIGURES.  XV 
CHAPTER   IX.— continued. 

PAGE 

FIG    60.     NADRAI  AQUEDUCT 205 

61.  NIRA  CANAL  SUPER-PASSAGE 209 

62.  RAVI  SYPHON 210 

63.  KAO  NULLAH  SYPHON 211 

64.  CHENAB  CANAL  SYPHON .211 

CHAPTER  XL 

65.  NILE  BANKS  ....'...,..  239 

CHAPTER  XIII. 

66.  ZIFTA  BARRAGE  LOCK,  PLAN        ......  265 

67.  ZIFTA,  BARRAGE  LOCK,  SECTION 265 

68.  ASSUAN  DAM  LOCK       ..*..*..  266 


INDEX 287 


IRRIGATION: 

ITS    PRINCIPLES   AND    PRACTICE   AS    A 
BRANCH    OF   ENGINEERING. 


CHAPTER  I. 

IRRIGATION   AND   ITS   EFFECTS. 

IRRIGATION  is  the  artificial  process  of  supplying  water  to 
crops  in  countries  where  the  rainfall  is  either  insufficient  or 
comes  at  the  wrong  season  for  their  cultivation.  Though 
agricultural  in  its  object,  it  has  now  become  a  special  branch 
of  engineering  on  account  of  the  nature  of  the  works  required 
for  the  control  of  water. 

The  inequalities  in  the  distribution  of  rainfall  are  not  only 
those  that  relate  to  time,  but  also  to  place.  The  rainfall  of  one 
region  may  be  abundant,  of  another  the  reverse.  The  rainfall 
of  certain  seasons  of  the  year  may  be  heavy,  while  that  of 
other  seasons  may  be  light  or  wanting  altogether.  In  some 
countries  the  inequalities  of  both  kinds  are  not  sufficiently 
pronounced  for  a  distinction  to  be  made  between  regions  of 
abundant  and  of  scant  rainfall,  and  between  rainy  and  dry 
seasons.  In  such  countries,  if  the  rainfall  exceeds  a  certain 
minimum,  irrigation  is  not  a  necessity  ;  England  and  the  north 
of  France  are  under  such  conditions. 

In  India  the  variations  of  rainfall,  both  as  to  place  and  time, 
are  extreme.  In  Sind  and  parts  of  the  Punjab  the  average 

I.  B 


2  IRF^GATION. 

rainfall  of  the  year  is  3  inches  only;  in  the  Central  Pro- 
vinces the  annual  rainfall  is,  in  places,  from  50  to  60  inches ; 
while  in  the  mountains  of  the  west  coast  and  in  the  Himalayas 
it  varies  from  50  to  100  inches  and  is  sometimes  as  high  as 
150  inches.  The  distribution  in  time  is  as  unequal  as  the  distri- 
bution in  place.  In  the  Madras  Province  12  inches  of  rainfall, 
or  about  one  quarter  of  the  total  annual  amount,  is  sometimes 
recorded  in  twenty-four  hours. 

So  also  in  the  United  States  of  America,  the  conditions  of 
the  country  range  from  arid  to  humid  in  consequence  of  wide 
variations  in  the  rainfall. 

Egypt  may  be  selected  as  an  example  of  a  country  under 
extreme  conditions  of  another  sort :  it  has  neither  rainy  region 
nor  rainy  season,  and,  as  far  as  agriculture  is  concerned,  may 
be  reckoned  rainless.  But  hydrographically  it  should  not  be 
taken  alone.  Its  creation  and  continued  existence  is  due 
entirely  to  the  fact  that  it  is  a  portion  of  the  Nile  country, 
which  has  its  rainy  regions  in  Abyssinia  and  the  Sudan ;  and 
that  it  lies  on  the  track  of  the  run-off  of  the  rainfall.  It  is  this 
that  makes  irrigation  in  Egypt  possible.  So  it  is  with  all  irriga- 
tion systems — the  country  irrigated  must  lie  on  the  track  of  the 
run-off  of  the  rain  that  falls  in  the  catchment  area  to  which 
it  belongs.  For  rainfall  is  the  primary  source  of  all  irrigation, 
even  of  that  effected  from  wells. 

The  scientific  land  boundary  between  nations,  from  an 
irrigation  point  of  view  at  any  rate,  is  the  water-shed,  or  line 
separating  catchment  areas,  whether  it  be  mountain  ridges  or 
desert  wastes.  In  the  case  of  the  Nile  country  this  principle 
has  been  of  late  years  upheld  so  far  as  was  politically  possible, 
but  the  possession  of  the  upper  reaches  of  the  Blue  Nile  by 
Abyssinia  stands  in  the  way  of  any  project  for  utilising  Lake 
Tsana  as  a  storage  reservoir  for  the  benefit  of  the  Sudan  and 
Egypt,  to  which  hydrographically  it  belongs. 

The  water  that  is  utilised  for  irrigation  must  naturally  have 
fallen  as  rain  somewhere  in  the  catchment  area  above  the  point 


IRRIGATION    AND   ITS   EFFECTS.  3 

at  which  it  is  applied  to  the  land  surface.  There  are  some 
countries  which,  though  their  rainfall  is  so  small  as  to  be  an 
absolutely  negligible  factor  in  agriculture,  have  still  been 
renowned  for  their  prosperity,  for  wealth  of  crops,  and  for 
advanced  civilisation  in  days  long  past.  The  best  known 
instances  are  those  of  Egypt  and  Mesopotamia,  the  lands  of 
the  Nile  and  the  Euphrates.  Both  these  rivers  in  their  natural 
state  annually  flooded  the  lands  bordering  their  lower  reaches, 
so  that  the  rain  that  had  fallen  in  the  region  where  their  sources 
lie  was  spread  over  the  surface  of  the  country,  and  a  natural 
system  of  irrigation  by  inundation  resulted.  In  Egypt  this 
natural  inundation  was  assisted  and  controlled  by  artificial 
banks  and  means  of  regulation  with  such  success  that  in  the 
time  of  Joseph  "  all  countries  "  came  into  Egypt  to  buy  corn  ; 
and,  later  on,  the  land  of  the  Nile  became  the  granary  of  Rome. 
The  artificial  system  of  irrigation  which  grew  out  of  the 
natural  peculiarities  of  the  Nile  is  known  as  the  basin  system  ; 
and  is  to  be  found,  even  to-day,  on  a  vaster  scale  and  in  a  more 
elaborately  developed  stage  in  Egypt  than  anywhere  els^  in 
the  world.  It  was  under  this  system  that  Egypt  attained  to 
the  heights  of  civilisation  which  it  reached  under  the  Pharaohs 
of  the  old  dynasties. 

But  the  evolution  of  the  Chaldean  civilisation  seems  to  have 
advanced  along  other  lines.  For,  though  it  is  probable  that 
the  newly  arrived  descendants  of  Noah  found  the  plain  in  the 
land  of  Shinar  dependent  for  its  agriculture  on  the  annually 
recurring  floods  of  the  Tigris  and  Euphrates,  and  that  they, 
their  predecessors  or  successors  may  have  introduced  some 
artificial  control  of  the  natural  inundation,  as  the  Egyptians 
did,  still  it  is  improbable  that  the  later  prosperity  of  Babylonia 
in  the  time  of  Nebuchadnezzar  was  the  result  of  basin  irrigation. 
In  Egypt  the  flood  season  is  sufficiently  early  to  allow  time  for 
the  maturing  of  a  winter  crop  of  corn  or  clover,  sown  after  the 
subsidence  of  the  flood.  In  Mesopotamia  the  flood  season  is 
six  months  later,  so  that  when  the  waters  retire,  the  parching 

B  2 


4  IRRIGATION. 

summer  has  begun,  when  no  rain  falls  to  mitigate  the  scorching 
heat.  Under  the  extreme  conditions  of  heat  and  dryness 
which  prevail  in  summer,  it  would  be  lost  labour  to  sow  seed 
which,  though  it  might  germinate,  would  wither  away  before 
coming  to  maturity.  So  that  it  wrould  seem  that  the  fertility 
of  the  country  and  the  opulence  of  its  cities,  as  described  in 
Hammurabi's  inscription  (B.C.  2200),  in  the  Bible,  and  also  by 
Herodotus,  must  be  ascribed  to  the  introduction  and  develop- 
ment of  a  system  of  perennial  irrigation  such  as  we  are  now 
pleased  to  call  "modern."  The  material  traces  of  the  canals 
still  exist,  and  testify  to  the  enterprise  and  skill  of  the  hydraulic 
engineers  of  Chaldea.  Hammurabi,  one  of  the  greatest 
monarchs  of  Babylonia's  history,  and  perhaps  a  contemporary 
of  Abraham,  thus  describes  in  an  inscription,  older  than  the 
Bible  record,  the  effect  of  irrigation  in  ancient  Chaldea: — 

"  I  have  made  the  canal  of  Hammurabi,  a  blessing  for  the 
people  of  Shumir  and  Accad.  I  have  distributed  the  waters 
by  branch  canals  over  the  desert  plains.  I  have  made  water 
flow  in  the  dry  channels,  and  have  given  an  unfailing''  (perennial) 
"  supply  to  the  people.  ...  I  have  changed  desert  plains  into 
well-watered  lands.  I  have  given  them  fertility  and  plenty, 
and  made  them  the  abode  of  happiness." 

Such  results  we  shall  find  attend  irrigation  wherever  it  is 
introduced.  Fertility  and  plenty  is  the  sure  return.  And 
neglect  of  the  canal  works  as  surely  brings  ruin.  The  basis  of 
Babylonia's  prosperity  and  the  cause  of  her  decline  appear  to 
be  indicated  in  the  following  passages  from  the  Bible  (Jer.  li. 
13,  42  and  43)  : — 

"  O  thou  that  dwellest  upon  many  waters,  abundant  in 
treasures,  thine  end  is  come.  .  .  ." 

"  The  sea  is  come  up  upon  Babylon :  she  is  covered  with 
the  multitude  of  the  waves  thereof;  her  cities  are  become  a 
desolation,  a  dry  land,  and  a  desert." 

It  is  doing  no  violence  to  the  text  to  assert  that  "  the  sea  " 
in  this  connection  is  the  Euphrates  in  flood.  In  Crnden's 


IRRIGATION    AND   ITS   EFFECTS.  5 

"Concordance"  (1817)  under  "Sea"  is  to  be  found  this  explana- 
tion :  "  The  Arabians,  and  Orientals  in  general,  sometimes 
give  the  name  of  sea  to  great  rivers,  as  the  Nile,  the  Euphrates, 
the  Tigris,  and  others,  which  by  their  magnitude,  and  by  the 
extent  of  their  overflowings,  seem  as  little  seas  or  great  lakes. 
Hence  the  country  of  Babylon,  which  was  watered  by  the 
Euphrates,  iscalled  'thedesert  of  the  sea'  (Isa.xxi.  i).  Jeremiah 
speaks  of  it  in  the  same  manner  (Jer.  li.  36) :  '  I  will  dry 
up  her  sea,  and  make  her  springs  dry.'  "  The  Egyptians  to-day 
call  the  Nile  the  Bahr  el  Azam,  the  most  excellent  sea. 
Shurippak,  the  city  where  Hasisatra,  the  Noah  of  the  Chaldean 
Deluge,  received  his  orders  to  build  a  ship  to  save  him  in  the 
coming  flood,  was  on  the  banks  of  the  Euphrates.  So  that 
the  earliest  record  of  any  flood  was  of  one  in  the  Euphrates 
valley. 

The  latter  of  the  two  verses  quoted  above  is  remarkable  for 
stating  that  a  flood  of  waters  had  for  result  "dry  land  and  a 
desert."  A  passage  in  the  Memoirs  of  Commander  Felix  Jones, 
of  the  Indian  navy,  quoted  in  a  lecture  delivered  by  Sir 
William  Willcocks  on  March  25th,  1903,  in  Cairo,  on  the 
"  Re-creation  of  Chaldea,"  is  in  striking  agreement  with  this 
text,  and  goes  far  to  explain  it.  The  passage  is  this : — 

"  The  summit  of  Opis,1  as  we  gaze  around,  affords  a  picture 
of  wreck  that  could  scarcely  be  conceived,  if  it  were  not  spread 
at  the  feet  of  the  beholder.  Close  to  us  are  the  dismembered 
walls  of  the  great  city,  and  many  other  mounds  of  adjacent 
edifices,  spread  like  islands  over  the  vast  plain,  which  is  as 
bare  of  vegetation  as  a  snow  tract,  and  smooth  and  glasslike 
as  a  calm  sea.  This  appearance  of  the  country  denotes  that 
some  sudden  and  overwhelming  mass  of  water  must  have  pros- 
trated everything  in  its  way,  while  the  Tigris,  as  it  anciently 
flowed,  is  seen  to  have  left  its  channel,  and  to  have  taken  its 
present  course  through  the  most  flourishing  portion  of  the 

1  The  ruins  of  Opis  are  on  the  Tigris  above  Baghdad,  at  the  point  where 
the  head  works  of  the  ancient  canals  would  have  been  situate. 


6  IRRIGATION. 

district,  severing  in  its  mad  career  the  neck  of  the  great 
Nahrwan  artery,  and  spreading  devastation  over  the  whole 
district  around.  Towns,  villages  and  canals,  men,  animals  and 
cultivation,  must  thus  have  been  engulfed  in  a  moment,  but 
the  immediate  loss  was  doubtless  small,  compared  with  the 
misery  and  gloom  that  followed.  The  whole  region  for  a  space 
of  250  miles,  averaging  about  twenty  in  breadth,  Nvas  depen- 
dent on  the  conduit  for  water,  and  contained  a  population  so 
dense,  if  we  may  judge  from  the  ruins  and  great  works 
traversing  it  in  its  whole  extent,  that  no  spot  in  the  globe 
perhaps  could  excel  it.  Of  those  who  were  spared  to  witness 
the  sad  effects  of  the  disaster,  thousands — perhaps  millions — 
had  to  fly  to  the  banks  of  the  Tigris  for  the  immediate  preser- 
vation of  life,  as  the  region  at  once  became  a  desert,  where 
before  were  animation  and  prosperity." 

Thus  Mesopotamia  furnishes  an  example  of  a  country  which 
flourished  exceedingly  by  reason  of  its  irrigation  works,  and 
fell  to  utter  ruin  when  these  works  were  overwhelmed.  Some 
day,  in  the  fulness  of  time,  the  successors  of  the  Chaldean 
engineers  will  lay  firm  hands  upon  the  twin  rivers  and  compel 
them  to  the  service  of  the  lands  through  which  they  flow,  that 
the  good  that  has  been  may  be  again  when  the  time  of 
regeneration  shall  come.  Already  a  beginning  has  been  made. 

Egypt  also,  when  the  British  Occupation  oegan  in  1882,  was 
found  to  be  suffering  from  the  inefficiency  of  its  engineers 
and  from  the  decay  of  its  irrigation  works  ;  but  the  latter  had 
not  reached  the  state  of  ruin,  past  repair,  in  which  the  ancient 
structures  of  Mesopotamia  are  now  found.  Still,  the  country 
was  in  a  bad  way  and  going  from  bad  to  worse,  when  those  who 
were  called  in  to  prescribe  recognised  that,  for  a  country  that 
was  wholly  agricultural  and  whose  agriculture  was  entirely 
dependent  on  irrigation,  the  one  thing  needful  was  efficiency  in 
its  irrigation  service.  The  story  of  Egypt's  recuperation  cannot 
be  told  here,  but  the  first  twenty  years'  results  which  followed  the 
substitution  of  efficiency  for  inefficiency  in  the  control  of  the  Nile 


IRRIGATION   AND  ITS   EFFECTS.  7 

waters  may  be  enumerated  in  general  terms  as  follows  : — The 
cotton  crop,  the  modern  source  of  Egypt's  wealth,  increased 
from  3,000,000  to  6,000,000  cwt,  or  in  value  from  £7,500,000 
to  £15,000,000  ;  the  maturing  of  the  maize — the  peasant's  food 
crop — was  assured  by  its  timely  sowing  being  made  a  certainty  ; 
the  cost  of  raising  crops  was  lessened  by  improved  means  of 
irrigating  them;  the  cultivable  area 'was  increased  from 
5,000,000  to  6,000,000  acres  ;  the  value  of  land  was  more  than 
doubled  ;  and  the  system  of  forced  and  unpaid  labour,  with  its 
attendant  abuses,  was  abolished.  The  capital  expenditure 
which  produced  these  results  was  about  £4,000,000.  This 
figure  does  not  include  the  expenditure  on  the  Assuan  dam  and 
other  works  connected  with  it,  the  construction  of  which  came 
after  the  realisation  of  the  benefits  enumerated.  The  further 
development  of  Egypt  which  has  resulted  from  these  later 
works  is  covered  by  the  summary  given  in  Note  i  of 
Appendix  IV. 

The  historical  record  of  irrigation  in  India  does  not  go  so  far 
back  as  that  of  Mesopotamia  or  Egypt.  It  was  about  300  B.C. 
that  Megasthenes,  writing  of  India,  referred  to  the  advantage 
of  double  crops  resulting  from  irrigation,  whereas  the  cunei- 
form inscription  of  Hammurabi,  already  quoted,  furnishes 
evidence  of  the  practice  of  irrigation  in  Babylonia  as  far  back 
as  2200  B.C.  ;  and  the  hieroglyphic  records  of  the  Pharaohs  of 
the  twelfth  dynasty,  of  date  about  2500  B.C.,  do  the  same  for 
Egypt. 

But  it  is  modern  results  which  are  of  present  interest  from  a 
practical  point  of  view.  As  one  of  the  most  recent  construc- 
tions, the  Lower  Chenab  Canal  is  a  noteworthy  example. 
Mr.  R.  B.  Buckley,  in  "  The  Irrigation  Works  of  India,"  thus 
describes  the  effect  of  its  construction  : — 

"  The  tract  which  it  commands,  known  as  the  Rechna  Doab, 
is  nearly  all  Crown  land.  Before  the  construction  of  the  canal 
it  was  entirely  waste,  with  an  extremely  small  population, 
which  was  mostly  nomad.  Some  portion  of  the  country  was 


8  IRRIGATION. 

wooded  with  jungle  trees,  some  was  covered  with  small  scrub 
camel  thorn,  and  large  tracts  were  absolutely  bare,  producing 
only,  on  occasions,  a  brilliant  mirage  of  unbounded  sheets  of 
fictitious  water.  Such  was  the  country  into  which  400  miles 
of  main  canals  and  1,200  miles  of  distributaries  now  distribute 
the  waters  of  the  Chenab,  turning  some  2,000,000  acres  of 
wilderness  into  sheets  of  luxuriant  crops.  .  .  .  About  1,500,000 
acres  of  the  Crown  lands  have  now  been  allotted  to  colonists, 
and  a  new  population  of  a  million  people  have  founded  home- 
steads which  they  cultivate  with  the  waters  of  the  Chenab 
Canal." 

Considering  India  as  a  whole,  the  result  of  the  work  done  by 
the  engineers  of  the  British  Government  during  the  past  sixty 
years  is  an  increase  of  the  area  watered  by  Government  irriga- 
tion works  from  3,000,000  or  4,000,000  to  26,000,000  acres, 
brought  about  by  a  capital  expenditure  of  7,124  lakhs  of 
rupees,  on  which  the  net  profit  amounts  to  8*8  per  cent.  This 
takes  no  account  of  the  indirect  profits.  The  value  of  the 
crops  raised  is  estimated  at  9,198  lakhs  of  rupees,  or  138  per 
cent,  of  the  capital  expenditure  on  the  canals  by  which  they 
are  irrigated.  But  this  must  not  all  be  written  down  to  the 
credit  of  irrigation,  as  the  crops  in  India,  in  most  cases,  are 
not  entirely  dependent  on  canal  water,  as  they  are  in  Egypt, 
and,  except  in  years  of  drought,  there  would  not  be  total  failure 
of  the  crops,  even  if  the  canal  supply  were  entirely  cut  off.  It 
is  generally  reckoned  in  India  that  irrigation  increases  the  gross 
outturn  by  about  30  per  cent.  The  Lower  Chenab  Canal  is  an 
exceptional  case  in  which,  perhaps,  the  whole  yield,  or  almost 
the  whole,  may  be  credited  to  the  canal.1  Exception  also  has 
already  been  made  of  years  of  drought.  A  canal  system  serving 
a  tract  which  is  severely  affected  by  a  serious  deficiency  in  the 
rainfall  may  in  a  single  year  save  crops  equal  in  value  to  its 
entire  capital  cost. 

The  result  of  irrigation  in  the  United  States  is  thus  described 
by  Mr.  Elwood  Mead  in  his  paper  read  at  the  International 
1  See  Note  2,  Appendix  IV. 


IRRIGATION   AND   ITS   EFFECTS.  9 

Engineering  Congress  of  1904  :  "  Since  1900  the  arid  region 
has  enjoyed  great  prosperity.  There  has  been  an  increase  in 
western  settlement,  and  the  values  of  both  land  and  water  have 
had  rapid  and  continued  advance.  Land  in  the  Yakima  valley, 
Washington,  which  could  have  been  purchased  five  years  ago 
for  $15  an  acre,  now  sells  for  $75  an  acre.  Land  in  the 
Turlock  and  Modesto  districts,  in  California,  which  sold  for  $20 
an  acre  three  years  ago,  now  brings  $60  an  acre.  Water  rights 
in  Idaho,  which  in  1894  found  no  buyers  at  $10  an  acre,  now 
have  prompt  sale  at  $25  an  acre." 

In  a  work  entitled  "  Irrigation  in  the  United  States,"  by 
Newell,  published  in  1902,  the  following  information  is  given : 
The  arid  regions,  which  include  two-fifths  of  the  area  of  the 
United  States,  have  an  average  annual  rainfall  of  20  inches  or 
less.  Of  the  arid  land  and  semi-arid  regions  470,000,000  acres 
is  grazing  land ;  but  it  appears  that  the  actual  amount  of  land 
which  is  irrigable  is,  as  variously  estimated,  from  60,000,000  to 
100,000,000  acres — a  field  for  irrigation  of  extent  sufficient  at 
least  to  satisfy  the  present  generation.  The  arid  regions 
extend,  moreover,  southward  into  Mexico  and  northward  into 
Canada,  so  that  in  these  two  countries  also  there  is  ample 
scope  for  irrigation  engineering.  Mr.  Newell  states  that 
twenty  to  thirty  acres  of  open  range  in  the  arid  regions  is 
generally  considered  sufficient  for  the  support  of  a  cow,  and 
that  the  same  land  under  irrigation  will  feed  ten  cows.  This 
agrees  with  the  experience  in  England,  where  rain  takes  the 
place  of  irrigation,  the  association  of  three  acres  and  a  cow 
being  familiar  to  politicians  as  well  as  farmers.  Mr.  Newell 
further  states  that  "  the  open  range  may  have  a  value  of  50 
cents  an  acre,  while  under  irrigation  the  selling  price  may 
rise  to  $50  per  acre,  or  even  f  500  per  acre  when  in  orchard." 

In  a  paper  on  "  Irrigation  in  the  Transvaal,"  by  M.  R. 
Collins,  published  during  1906  in  Vol.  CLXV.  of  the  Pro- 
ceedings of  the  Institution  of  Civil  Engineers,  it  is  stated,  with 
reference  to  the  value  of  land  in  the  Transvaal,  that  "  a  liberal 


10  IRRIGATION. 

estimate  of  the  value  of  good  unirrigated  land  would  be  £3  to 
£5  per  acre.  Each  acre  of  land  is  enhanced  in  value  by  £25 
by  being  brought  under  irrigation." 

In  Europe  the  countries  that  practise  irrigation  are  France, 
Italy  and  Spain. 

In  Northern  and  Central  France  irrigation  is  not  a  necessity 
for  raising  crops,  but  it  is,  all  the  same,  taken  advantage  of  to 
increase  the  fertility  of  meadow  lands  for  hay  crops.  The 
prosperity  of  Normandy,  for  instance,  is  due  to  regular  irriga- 
tion. In  Southern  France,  however,  where  the  summers  are 
very  dry  and  hot,  irrigation  is  useful,  if  not  indispensable,  for 
all  kinds  of  cultivation,  particularly  meadows.  Market  garden- 
ing is  impossible  without  it.  It  has  been  estimated  that 
irrigation  in  France  brings  an  increase  in  net  earnings  of  at 
least  200  francs  per  hectare  (£3  75.  6d.  per  acre).  Sir  Colin 
Scott-Moncrieff  states,  in  "  Irrigation  in  Southern  Europe,"  1868, 
that  "  in  Vaucluse,  in  the  south  of  France,  the  rental  of  good 
land  not  entitled  to  irrigation  is  about  £3  45.,  and,  if  it  can 
procure  it,  it  rises  to  about  £4  35.  per  acre  " ;  and  further  adds 
that  irrigation  causes  an  increase  of  50  per  cent,  in  the  price  of 
land. 

Italy  is  the  country  of  irrigation  in  its  most  advanced  stage 
of  development.  The  plains  of  Piedmont  and  Lombardy  pro- 
vide material  for  the  liberal  education  of  an  irrigation  engineer, 
and  show  what  artificial  control  of  the  natural  water  supplies 
of  a  country,  in  competent  hands,  is  capable  of  effecting. 

Lastly,  there  is  Spain.  As  Italy  owes  much  of  its  irrigation 
laws  and  customs  to  the  ancient  Romans,  so  is  Spain  indebted 
to  the  Moors.  Valencia,  Murcia  and  Granada,  Elche  and 
Lorca,  had  Moors  for  their  first  irrigation  engineers,  whose 
works  remain,  active  and  beneficent,  in  the  hands  of  the 
conquerors  who  expelled  the  enterprising  race  that  constructed 
them.  The  irrigation  works  of  Valencia  are  supposed  to  have 
been  executed  about  A.D.  800.  For  nearly  three  hundred  years 
after  the  final  expulsion  of  the  Moors  from  their  last  stronghold 


IRRIGATION    AND   ITS   EFFECTS.  II 

of  Granada  little  was  done  by  the  Spaniards  to  extend  the  area 
of  irrigation.  But  during  the  reign  of  Charles  III.,  A.D.  1785 
to  1791,  dams  were  built  for  the  storage  of  water  and  a  fresh 
impulse  given  to  irrigation.  The  dams  of  Spain  vary  in  height 
from  21  to  48  metres  (69  to  157  feet). 

The  result  of  irrigation  in  Spain  on  land  values  is  remarkable.1 
From  certified  copies  of  sales  during  the  year  1859  the  following 
appears :  The  average  price  of  irrigated  ground  at  Castellon 
was  £140  per  acre,  the  average  price  of  the  ground  without 
irrigation  in  the  same  neighbourhood  being  £10.  In  Murcia 
the  price  of  irrigated  land  was  £500  per  acre,  of  ground  without 
irrigation  £25  to  £30.  Near  Madrid  irrigated  land  was  leased 
for  £5  an  acre,  while  unirrigated  land  could  be  bought  outright 
for  that  figure.  As  a  rule,  for  the  whole  of  Spain,  good  land 
without  irrigation  in  the  valleys  could  be  bought  at  an  average 
price  of  from  £6  to  ;£io,  and  the  same  land  irrigated  at  £80  to 
£120  per  acre. 

It  is  thus  abundantly  evident  that,  where  rainfall  is  deficient 
or  capricious,  but  the  soil  is  cultivable,  irrigation  is  a  most 
potent  agent  for  converting  land,  of  little  value  without  it,  into 
valuable  property;  that  a  well-administered  system  of  irrigation 
may  double  the  value  of  property  that  has  hitherto  been  served 
by  a  badly  managed  system ;  and  that  in  a  country  dependent 
on  irrigation,  the  neglect  to  maintain  its  canal  works  in  a  state 
of  efficiency  will  result  in  its  impoverishment  and  ultimate 
ruin. 

1  Proceedings  of  Inst.  C.E.,  "  Irrigation  in  Spain,"  by  Higgin  (1869). 


CHAPTER  II. 

BASIN    IRRIGATION. 

THE  earliest  form  of  irrigation  was  probably  a  natural  one, 
brought  about  by  rivers  overflowing  their  banks  during  seasons 
of  flood.  Egypt,  on  the  Nile,  and  Mesopotamia,  on  the  Tigris  and 
Euphrates,  have  already  been  cited  as  countries  in  which  the 
genesis  of  irrigation  was  probably  of  such  a  kind.  Sind,  on  the 
Indus  in  India,  is  another  notable  instance.  Most  rivers  with 
periodical  flood  seasons  have  their  sources  in  mountain  ranges, 
where  the  rainfall  is  heavy  and  the  ground  is  rocky.  In  such 
cases  the  declivity  of  a  river  is,  at  first,  very  great,  and  the 
velocity  of  the  stream  is  torrential.  The  detritus,  which  is 
washed  down  from  the  steep  slopes  of  the  hills  and  eroded  from 
the  bed,  is  carried  forward  to  the  point  beyond  the  foot  of  the 
hills  where  the  slope  of  the  stream  becomes  reduced.  Here 
erosion  ceases  and  deposition  of  the  heavier  detritus  commences. 
Fan-shaped  layers  of  deposits  spread  themselves  out,  and,  in 
process  of  time,  force  the  stream  to  take  a  new  course.  Again 
the  depositing  process  is  repeated  until  the  general  country 
level  is  raised.  At  length  the  stream  cuts  a  way  through  its 
own  deposits  down,  perhaps,  to  bed-rock,  and  flows  forward  in  a 
deep  channel  through  the  softer  plains.  Gradually  the  velocity 
becomes  less  rapid  and  the  channel  less  deep  as  the  water 
flows  seawards,  until  at  length  the  river  enters  the  region  where 
it  overflows  its  banks  in  flood. 

From  that  point  onwards  the  bed  of  the  river  and  the  lands 
alongside  are  being  gradually  raised  by  the  material  brought 
down  by  the  water,  while  the  delta  of  the  river  is  being  con- 
stantly added  to  along  its  seaward  margin  by  the  deposit  of  the 


BASIN   IRRIGATION.  13 

annual  flood.     When  the  river  tops  its  natural  banks  and  the 
flood  waters  leave  its  channel,  the  velocity  of  flow  of  the  escap- 
ing water  rapidly  diminishes,  and,  in  consequence,  the  silt  in 
suspension   is   deposited  in   greatest   quantity  within  a  short 
distance  from  the  river  edge ;  so  that,  in  course  of  time,  the 
lands  assume  a  downward  slope  away  from  the  river.     This  is 
the  explanation  of  the  fact  that,  in  the  case  of  wide  flat  valleys 
traversed  by  rivers  with  a  periodical  overflow,  the  highest  land 
is  found  along  the  river  edge.     If  there  are  several  branches 
traversing  a  level  delta,  the  surface  slope  will  be  away  from 
each  until  it  meets  the  slope  formed  under  the  influence  of  the 
adjacent  channel.     Along  the  meeting  line  an  escape  channel 
will  probably  be  formed  by  the  flow-off  of  the  flood  waters, 
which  takes  place  when  the  river  falls.     The  delta  of  Egypt 
and  the  deltas  of  India  furnish  examples  of  this  formation,  the 
further  development  of  which  has  been  arrested  by  the  con- 
struction of  protective  banks  to  guard  the  irrigated  crops  from 
being  damaged  by  flood.     The  Nile  valley  of  Upper  Egypt 
exhibits  this  characteristic  in  its  simplest  form.     The  single 
channel  of  the  river  traverses  the  valley,  and  its  floods  spread 
sideways  over  the  land  on  either  side  of  it.     There  is  thus 
formed  a  land  surface  of  the  form  shown  to  an  exaggerated 
scale  in  Fig.  i.     In  such  a  valley  as  that  of  the  Nile  in  Upper 
Egypt  the  flood  waters  of  an  inundation,  if  uncontrolled  by 
artificial  works,  would  move  forwards  over  the  land  as  a  shallow 
sheet  of  water  with  its  surface  lower  than  the  river  level  opposite, 
and  only  partially  submerging  the  land.    In  very  extreme  floods, 
however,  the  level  of  the  inundation  would  be  everywhere  the 
same  as  that  of  the  river  alongside.     There  would  be  certain 
lengths  of  the  high  margins  of  the  river  lower  than  other  parts, 
and,  over  these,  ordinary  floods  would  find  their  way  to  the  lower 
land  beyond ;  but  the  highest  floods  would  overtop  the  river 
margin  everywhere.     A  low  flood  would  probably  not  find  its 
way  to  the  low  land  at  all,  except  in  small  quantity  through 
natural  channels  formed  by  the  waters  of  previous  high  floods 


14  IRRIGATION 

cutting  their  way  back  to  the  river.  The  first  thing  that  would 
occur  to  the  inhabitants  as  a  method  of  securing  an  inundation, 
whether  the  flood  were  low  or  high,  would  be  to  make  cuts 
through  the  high  land  along  the  river  edge,  whereby  water 
would  be  admitted  to  the  more  remote  lands  below  flood  level. 
They  would  then  endeavour  to  make  the  water  rise  over  the 
higher  lands  by  placing  obstructions  in  the  way  of  the  forward 

INUNDATION        DIAGRAMS 


FIQ    1 


flow  of  the  water  thus  introduced  to  the  lower  lands.  By  some 
such  process  as  this,  short  inundation  canals  and  cross  embank- 
ments would  come  into  being.  Then,  to  prevent  the  cross 
embankments  from  being  swept  away  by  the  effects  of  a  high 
flood,  a  protective  bank  along  the  river  edge,  to  exclude  excess, 
would  be  felt  to  be  a  necessity. 

But   with   such  arrangements  the  inundation  of  the   com- 
paratively high  land  near  the  river  would  have  been  a  constant 


BASIN   IRRIGATION.  15 

difficulty,  necessitating  inconveniently  high  cross  embankments 
to  hold  the  water  up  sufficiently.  On  this  account  the  advan- 
tage of  separating  this  width  from  the  remainder,  and  of 
providing  for  its  irrigation  by  independent  canals,  would  have 
suggested  itself.  For  this  purpose  a  longitudinal  bank  would 
be  made  along  the  line  where  the  comparatively  steep  slope 
near  the  river  changes  to  the  flatter  slope  of  the  more  remote 
land.  The  strip  alongside  the  river,  thus  separated  from  the 
lower  lands,  would  be  given  its  own  canal,  in  which  the  water 
would  be  held  up  to  the  maximum  level  that  the  flood  in  the 

IMPERFECT     BASIN      SYSTEM 


F  I  Q      3 


river  could  produce.     The  result,  in  a  favourable  flood,  would 
be  as  shown  in  Fig.  2. 

In  the  chain  of  basins  along  the  lower  land  arrangements 
would  have  to  be  made  to  pass  on  the  water  from  basin  to  basin. 
At  first  this  would  be  done  by  means  of  openings  (by  washes)  at 
the  ends  of  the  banks  on  the  higher  ground,  protected  probably 
by  loose  stone  Cuts  would  be  made  in  the  banks,  along  the 
line  of  flow-off  in  the  lowest  land,  when  it  was  desired  to  finally 
get  rid  of  the  water.  These  cuts  would  later  on  be  replaced  by 
masonry  regulators  and  escapes  to  give  better  control.  There 
would  thus  be  created  a  system  of  basins  arranged  as  in  Fig.  3. 
This  figure  will  serve  to  illustrate  the  defects  of  the  arrange- 
ments when  the  basin  system  had  reached  this  stage  of  evolution,, 


l6  IRRIGATION. 

Y,  Y,  Y  are  the  main  basins  of  a  chain ;  X  the  terminal 
basin  of  the  next  chain  above ;  Z  the  initial  basin  of  the  chain 
next  below  the  Y  chain.  The  smaller  basins  y,  y,  y  are 
those  which  include  the  high  margin  of  the  river.  The  main 
basin-feeder  discharges  into  the  first  basin  Y,  from  which  the 
water  is  passed  on  to  the  other  basins  in  succession.  The  level 
in  each  basin  is  so  regulated  by  the  escapes  in  the  cross 
embankments  that  the  water  may  cover  the  highest  land  ;  and 
thus  a  succession  of  water  terraces  is  formed.  The  escape  E 
at  the  tail  of  the  chain  passes  any  excess  there  may  be  back 
into  the  river  and  provides  for  the  final  emptying.  The 
smaller  basins  y,  y,  y  are  worked  in  a  similar  way. 

Now,  in  arranging  for  the  supply  of  water  to  a  basin  system, 
there  are  two 'important  principles  to  be  observed.  The  first 
is  that,  in  a  year  of  low  flood,  the  supply  should  be  delivered  in 
such  quantity  and  at  such  levels  that  the  whole  of  the  land 
may  be  submerged  during  the  period  of  flood  to  the  extent  that 
saturates  it  sufficiently  to  secure  that  the  crop,  which  will  be 
sown  after  the  flood,  shall  germinate  and  come  to  maturity 
without  further  irrigation.  The  second  principle  is  that  full 
advantage  should  be  taken  of  a  good  flood  to  enrich  the  soil  by 
encouraging  the  deposit  of  the  fertilising  matter  which  the  river 
brings  down  in  suspension  from  its  sources;  and  that  this 
deposit  should  not  only  be  as  abundant  as  possible,  but 
should  be  evenly  distributed  over  the  whole  area  of  the  chain  of 
basins. 

In  the  scheme  depicted  in  Fig.  3  these  two  principles  are  not 
observed.  The  chain  of  basins  Y,  Y  might  perhaps  in  a  low 
flood  get  filled  by  water  passed  on  from  X  ;  but  the  case  of  the 
smaller  basins  y,  y  would  be  hopeless  without  a  syphon  con- 
necting the  high-level  canal  with  the  upper  system  X,  as  shown 
by  the  dotted  line. 

The  second  principle  enunciated,  concerning  the  distribution 
of  muddy  flood  water,  has  next  to  be  considered.  It  is  con- 
ceivable that  the  high-level  canal  will  satisfy  this  principle  in  a 


BASIN    IRRIGATION.  !/ 

high  flood ;  in  a  low  flood,  without  a  syphon  connection  with 
the  upper  chain,  it  will  not  flow  at  all.  But  the  main  basin- 
feeder  is  altogether  out  of  order.  It  discharges  into  the  first 
basin  from  a  channel  without  banks,  and  creates  a  shallow  lake 
from  which  the  second  basin  is  fed  through  the  cross  embank- 
ment. In  the  same  way  the  third  is  fed  from  the  second,  the 
fourth  from  the  third,  and  so  on.  Consequently  the  first  basin 
gets  most  of  the  muddy  deposit  and  the  lowest  basin  the  least. 
An  arrangement  of  canals  and  banks  in  a  basin  chain,  which 
pays  due  regard  to  the  principles  laid  down,  is  shown  in  Fig.  4, 

IMPROVED      BASIN       SYSTEM 


F  I   Q       4 


The  main  basin-feeder,  instead  of  discharging  into  the  first 
basin,  passes  by  it  between  banks,  and  is  carried,  approximately, 
along  the  same  alignment  as  the  bank  of  Fig.  3  which  separates 
the  high  and  low  basins.  At  the  upper  corner  of  each  basin  is 
a  feeder-sluice  to  fill  the  basin  and  give  it  muddy  water,  so  that 
all  may  get  a  fair  share  of  the  fertilising  matter.  The  masonry 
works  situated  in  the  banks  of  the  basins,  at  the  points  where 
they  cross  the  natural  drainage  line,  serve  to  regulate  the  basin 
levels  and  to  empty  the  basins  at  the  proper  time;  also  to 
connect  one  chain  with  the  next  one  above  and  below,  so  that 
water  can  be  passed  from  one  chain  to  another  when  it  is 
advantageous  to  do  so, 

I.  0 


18  IRRIGATION. 

By  means  of  the  syphon  canal,  high  level  water,  derived  from 
a  point  on  the  river  at  a  considerable  distance  up-stream,  is 
furnished  to  the  lands  beyond  the  basin-feeder,  which,  without 
it,  would  be  dry  in  low  flood  years.  Though  this  arrangement 
secures  water  to  the  high  level  tract,  the  old  direct  heads  from 
the  river  should  not  be  suppressed,  as  in  high  floods  it  is  of 
advantage  to  admit  a  supply  through  them  on  account  of  the 
increase  of  fertilising  deposit  to  be  obtained  by  so  doing.  All 
the  old  direct  feeders  of  short  run  should  be  maintained  with 
the  object  of  so  using  them  that  full  advantage  may  be  taken  of 
high  floods  when  they  come. 

If  a  chain  of  basins  can  be  linked  up  with  the  chain  next 
above  it,  the  canals  of  the  upper  chain  can  be  so  disposed  and 
designed  as  to  effect  the  inundation  of  all  the  lands  as  far  down 
as  the  point  where  the  water  of  the  main  feeder  of  the  lower 
chain  comes  to  country  surface.  But,  if  a  chain  of  basins  is  in 
the  unfortunate  position  of  having  no  chain  above  it,  there  will 
be  land  on  either  side  of  its  main  feeder,  from  its  off-take  on 
the  river  to  the  point  where  its  water  comes  to  country  surface, 
which  cannot  be  flooded.  In  high  floods  the  unflooded  area 
may  be  little  or  nothing  ;  in  low  floods  it  may  be  considerable. 

The  selection  of  the  points  at  which  the  main  feeders  take 
off  depends  on  the  windings  of  the  river  and  the  configuration 
of  the  land  to  be  irrigated.  The  position  of  the  off-take  on  the 
river  has  a  great  influence  on  the  silting  tendencies  of  the  canal. 
The  original  constructors  of  the  inundation  canals  of  India 
found  that  it  was  best  to  take  off  at  points  screened  from  the 
full  force  of  the  current,  and,  therefore,  preferred  as  a  site  for 
the  head  of  an  inundation  canal  a  point  on  a  side  branch  of 
the  river  some  little  distance  above  its  lower  junction  with  the 
main  stream.  The  soundness  of  this  practice  is  confirmed  by 
v.he  case  of  a  canal  in  Egypt,  the  Abu  Bagara,  which  takes  off 
a  side  branch  of  the  Nile  near  its  lower  end,  and  is  the  only  old 
inundation  canal  in  Egypt  which  does  not  silt.  The  principles 
formerly  followed  by  the  Arab  engineers  in  Egypt  (as  stated  by 


BASIN   IRRIGATION.  19 

Colonel  J.  C.  Ross  in  "  Notes  on  the  Distribution  of  Water, 
and  the  Maintenance  of  Works  in  Upper  Egypt.  Cairo,  1892  ") 
are  opposed  to  the  original  Indian  practice,  being  as  follows : 
"  The  off-take  should  be  placed  in  the  bank  along  which  the 
deep  water  of  the  Nile  flowed."  This  rule  is  stated  in  a  form 
as  if  for  guidance,  but  it  lays  down  a  misleading  principle.  If 
the  Arab  engineers  are  correctly  credited  with  the  observance 
of  this  principle,  it  does  not  follow  that  they  are  worthy  of 
imitation,  for  neither  theory  nor  experience  lend  their  support 
to  the  soundness  of  this  practice.  Theoretically  the  most 
favourable  place  to  select  for  the  off-take  is  any  point  past 
which  the  river  flows  with  the  same  velocity  as  the  canal  will 
flow  after  the  water  is  drawn  into  it,  so  that  there  may  be  no 
change  of  velocity.  If  the  canal  has  its  off-take  so  situated, 
there  should  be  a  minimum  of  silt  deposit  in  the  canal  con- 
sistently with  a  maximum  of  silt  carried  forward  in  suspension 
to  the  fields.1  The  question  of  silt  deposit  will  be  discussed  in 
a  future  chapter,  when  it  will  be  shown  that  one  of  the  condi- 
tions of  bringing  about  a  diminution  of  silt  deposit  in  a  canal 
is  an  absence  of  high  velocity  in  the  river  at  the  point  of  off- 
take. 

The  site  of  the  off-take  having  been  decided  upon,  the  slope 
of  the  land  surface  determines  the  water  surface  slope  to  be 
adopted  in  the  feeder  canal.  Supposing  the  land  on  the  align- 
ment of  the  canal  to  have  a  slope  of  joimj>  *ne  canal  water 
surface  slope  might  be  ^oJnrr  The  statistics  of  previous  floods 
must  be  studied  to  determine  the  duration  of  the  flood  and  its 
levels.  In  order  that  the  inundation  may  not  fail  in  bad  years, 
the  project  should  be  based  on  the  levels  of  a  low  flood,  and  on 
the  period  during  which  the  canals  would  flow  to  effect  the 
filling  of  the  basins ;  remembering  that,  even  if  the  river  levels 
admitted  of  it,  the  filling  cannot  be  prolonged  beyond  a  certain 
date,  as  the  basins  must  be  emptied  and  the  land  surface  be 
prepared  to  receive  the  seed  of  the  coming  crop  before  it  is  too 
late  for  the  sowing.  In  Egypt  fifty  days  is  the  full  period  of 

1  See  Note  3,  Appendix  IV. 

c  * 


2O  IRRIGATION. 

filling.  The  mean  flood  level  of  this  period  is,  for  example, 
1-50  metres  (or,  say,  5  feet)  below  the  country  surface  at  the 
point  where  the  canal  takes  off  from  the  river.  If,  then,  the 
country  slope  is  Toioo»  and  the  canal  water  surface  slope 
2oooo>  the  water  will  come  to  land  surface  at  a  point  thirty 
kilometres  (19  miles)  from  the  canal  head,  as  shown  in  Fig.  5. 
Down  to  this  point,  then,  the  canals  of  the  upper  system  (if 
there  is  one)  must  be  carried,  and  the  land  must  be  considered 
as  belonging  to  the  upper  chain  for  the  purpose  of  calculating 
the  dimensions  of  canals. 

The  bed  level  of  the  feeder  canal  should  be  fixed  at  that  level 
below  the  average  level  of  the  flow  period  which  will  give  the 

FLOOD     CANAL     DIAGRAM 

c 


discharge  required  with  a  channel  of  a  convenient  bed  width. 
By  the  "  average  level  of  the  flow  period  "  is  meant  the  mean  of 
the  levels  of  the  flood  at  the  canal  head  between  the  date  that 
water  is  admitted  into  the  canal  to  feed  the  basins  and  the  date 
when  the  head  is  closed  to  shut  off  the  supply.  To  determine 
what  the  dimensions  of  the  canal  should  be,  a  calculation  must 
be  made  of  the  quantity  of  water  required  to  fill  the  basins 
depending  on  the  feeder,  lying  between  the  point  where  the 
water  comes  to  country  surface  and  the  point  where  the  water 
of  the  canal  in  'the  chain  next  below  does  the  same.  The 
inundation  should  be  of  such  proportions  that  the  highest 
ground  in  any  basin  would  be  covered  by  a  depth  of  at  least 
30  centimetres  (i  foot)  of  water.  The  basins  of  Egypt  vary  in 
size  from  3,000  to  50,000  acres ;  the  mean  depth  of  the  inunda- 
tion varies  from  f  metre  (2f  feet)  in  small  basins  to  i  j  metres 
(4!  feet)  in  large  basins.  But,  as  a  rough  estimate,  sufficiently 


BASIN    IRRIGATION.  21 

correct  when  we  are  dealing  with  principles,  5,000  cubic  metres 
(176,000  cubic  feet)  may  be  taken  as  the  quantity  required  per 
acre  of  land  to  be  flooded,  inclusive  of  the  quantity  required  to 
make  good  the  loss  by  evaporation  and  absorption  during  the 
period  of  inundation.  The  daily  discharge  of  the  main  feeder 
for  the  fifty  days'  period  of  flow  must,  therefore,  be  -g^th  of 
5,000  cubic  metres,  or  100  cubic  metres,  per  acre  to  be  flooded. 
The  mean  flood  level  of  the  fifty  days'  period,  used  as  one  of 
the  data  in  the  designing  of  the  canal,  need  not  be  that  of  an 
extreme  low  flood  such  as  comes  but  rarely,  as  in  such  years  a 
diminished  quantity  of  water  must  be  made  to  do  increased 
duty  by  bringing  each  basin  in  succession  up  to  full  inundation 
level  with  the  discharge  of  the  basin  next  above  in  order. 

The  bed  level  and  width  of  the  feeder  canal  can  then  be 
determined  with  these  data,  namely,  the  mean  flood  level,  the 
daily  discharge,  and  the  water  surface  slope  in  the  canal. 

To  deal  satisfactorily  with  the  large  bodies  of  water  that 
have  to  be  distributed  over  the  extensive  areas  of  a  chain  of 
basins  perfect  control  over  the  water  at  all  points  is  necessary. 
This  is  only  to  be  obtained  by  a  complete  system  of  regu- 
lating works,  such  as  head  sluices,  to  draw  the  water  from 
the  river  into  the  feeder  canal ;  basin  sluices,  to  admit 
water  from  the  canal  into  the  basins ;  regulators  in  the  basin 
cross  banks  to  pass  on  the  water  and  regulate  the  level  in  the 
basins  above  them ;  and  escapes  to  discharge  the  water  back 
into  the  river. 

If  the  head  sluice  of  the  feeder  canal  is  built  near  the  river 
edge,  it  may  be  in  danger  from  river  erosion :  for  this  reason  it 
is  generally  placed  at  some  little  distance  from  it,  in  spite  of 
the  objection  that  the  channel  up  stream  of  the  head  silts  up 
badly  when  the  head  is  closed.  It  is  sometimes  constructed 
on  the  top  of  the  syphon  which  carries  the  water  of  the  upper 
chain  under  the  main  feeder.  Such  an  arrangement  has  this 
to  recommend  it,  that  the  head  sluice  can  be  so  designed  that 
its  weight  may  resist  the  tendency  of  the  syphon  to  blow  up 


22  IRRIGATION. 

when  it  is  working  under  a  head ;  but  it  has  the  disadvantage 
that  the  design  is  necessarily  complicated,  and  it  is  difficult  to 
arrange  for  the  traffic  which  passes  across  the  canal  and  along 
its  banks. 

Again,  the  head  may  be  built  at  such  a  distance  down  stream 
of  the  syphon  as  to  allow  room  for  a  basin  escape  to  be  built 
between  the  two.  The  basin  chain  would  then  empty  itself  by 
the  escape  into  the  off-take  channel  of  the  feeder  canal,  by 
which,  if  the  head  sluice  openings  were  closed,  the  discharged 
water  would  find  its  way  into  the  river.  This  arrangement  is 
shown  at  F  in  Fig.  4. 

At  the  tail  end  of  the  chain  of  basins  the  main  escape  may 
be  either  situated  as  just  described  (F,  Fig.  4),  or  may  be 
placed  in  the  position  of  the  escape  from  basin  X  (Fig.  4).  This 
latter  arrangement  is  of  the  nature  of  a  level-crossing  over  the 
canal  leading  to  the  syphon.  In  the  left  bank  of  the  syphon 
canal  an  inlet  regulator  passes  the  basin  water  into  the  canal, 
and  an  escape  in  the  opposite  bank  discharges  it  into  the  river. 
The  syphon  down  stream  of  the  level-crossing  is  fitted  with 
regulating  apparatus,  so  that  the  syphon  canal  can  be  wholly  or 
partially  closed  at  will. 

The  discharging  capacity  of  the  main  escape  has  next  to  be 
considered.  The  quantity  of  water  to  be  finaJJy  discharged  at  the 
tail  of  a  chain  will  be  the  volume  contained  in  the  basins,  and  will 
be  less  than  the  estimated  quantity  required  for  the  filling  by  the 
amount  allowedfor  evaporation  and  absorption.  For  rough  calcu- 
lations it  has  been  the  custom  in  Egypt  to  estimate  the  quantity  to 
be  discharged  at  the  rate  of  4,000  cubic  metres  (141,000  cubic  feet) 
an  acre,  which  allows  nearly  a  metre  (or  3  feet)  as  the  mean 
depth  of  the  inundation.  But,  as  the  water  must  be  got  rid  of 
in  time  for  the  sowing  of  the  saturated  ground,  a  period  of 
only  about  twenty  days  can  be  allowed  for  the  emptying, 
against  fifty  days  for  the  filling,  and,  therefore,  the  tail  escape 
must  be  designed  to  effect  the  discharge  in  the  shorter  period. 
The  discharging  power  of  the  escape,  which  depends  on  the  river 
levels  at  the  time  of  discharge,  will  be  greater  when  the  river 


BASIN    IRRIGATION.  23 

is  low  than  when  it  is  high ;  whence  it  happens  that  in  good 
floods,  at  any  rate  if  they  are  late  in  falling,  the  escapes  work 
slowest  when  there  is  most  water  to  be  got  rid  of.  The  escape 
should,  therefore,  be  given  ample  water-way,  so  that  it  may 
prove  sufficient  under  adverse  conditions.  It  should  also  be 
given  an  extended  apron  and  ample  protection  of  well  revetted 
slopes  and  talus  of  heavy  pitching  down  stream,  as,  in  the 
opposite  case  of  a  low  river,  the  escape  will  have  to  work  for  a 
prolonged  period  under  the  severe  conditions  of  a  considerable 
head.  This  same  precaution  must  be  taken  in  the  case  of  the 
regulators  in  the  cross-embankments  of  the  basins,  as  they 
discharge  into  wide  expanses  requiring  an  enormous  volume  of 
water  to  affect  the  surface  level,  so  that  the  head  remains 
undiminished.  In  other  respects  the  design  of  such  works 
may  be  the  same  as  that  of  ordinary  regulators  ;  the  volume  of 
water  to  be  passed,  the  time  to  be  allowed  for  passing  it,  and 
the  head  under  which  the  discharge  will  be  effected  determining 
the  water-way  to  be  allowed  in  each  case. 

The  programme  of  operations  in  the  filling  and  emptying  of 
a  chain  of  basins  is,  in  general  terms,  somewhat  as  follows  : — 

On  a  fixed  date  (generally  August  loth  in  Upper  Egypt)  the 
basin  feeder  heads  are  opened,  and  the  basins  commence  to  fill. 
The  escapes  are  likewise  opened  so  as  to  admit  river  water  also 
by  them  into  those  basins  which  are  in  connection  with  the 
escape  channels ;  but,  as  soon  as  the  water  coming  from  above 
causes  a  reverse  flow  back  into  the  river,  the  escapes  are  closed 
again.  The  basin-filling  by  the  feeder  canal  continues  at  a  rate 
depending  on  the  river  levels.  At  the  same  time,  water  is  passed 
forward  into  the  canals  overlapping  the  feeder  of  the  next  chain. 

One  of  the  principles  laid  down  for  observance  in  the 
designing  and  working  of  a  basin  system  is  that  full  advantage 
should  be  taken  of  a  good  flood  to  obtain  the  maximum  deposit 
of  fertilising  matter  possible ;  and  one  way  of  doing  this  is  to 
pass  as  much  water  as  possible  through  the  basins.  To  effect 
this,  the  head  sluice  of  the  feeder  canal  should  not  be  closed 


24  IRRIGATION. 

when  the  basins  are  full,  but  should  be  left  open,  and  the  levels 
in  the  basins  regulated  by  the  opening  of  their  escapes  to  the 
necessary  extent.  In  this  way  a  quantity  of  water  is  admitted 
to  the  basins  in  excess  of  that  required  to  fill  them,  and,  as  the 
current  in  the  wide  expanse  of  water  is  imperceptible,  a  larger 
volume  of  silt  is  deposited  and  the  land  therefore  derives  greater 
benefit. 

In  fifty  days  after  the  first  admission  of  water,  or  less  if  the 
flood  is  a  good  one,  all  the  basin  land  should  be  under  water ; 
and  a  week  later  (October  5th)  the  basins  should  be  ready  to 
discharge.  The  feeder  heads  are  then  shut  down,  and  the 
supply  from  the  river  cut  off;  the  upper  basins  are  discharged 
on  to  the  lower  to  complete  their  inundation,  if  still  incomplete, 
and  the  water  passed  forward  from  basin  to  basin  to  the  tail  of 
the  chain,  where  it  is  finally  got  rid  of  through  the  escape  into 
the  river.  In  a  fortnight  or  three  weeks  the  basins  should  be 
empty,  with  the  exception  of  the  water  in  the  lowest  hollows 
which  drains  off  more  slowly.  The  seed  of  the  basin  crop 
— wheat,  beans  or  clover — is  then  scattered  broadcast  over  the 
surface  ooze  and  merely  pressed  into  it  by  a  plank  drawn  over 
the  ground ;  or  else,  after  a  short  interval  of  drying,  the  land  is 
lightly  scratched  with  a  plough  before  the  seed  is  scattered.  The 
crop  is  then  left  to  take  care  of  itself  till  it  is  ripe  for  harvest. 

Before  leaving  the  subject  of  basin  irrigation  it  may  be  useful 
to  note  the  dimensions  of  the  basin  banks  adopted  of  late  years 
in  Egypt.  The  principal  basin  banks,  and  the  river  bank,  have 
a  crest  width  of  5  metres  (16  feet)  and  side  slopes  of  2  of  base  to 
i  of  rise.  The  crest  level  is  made  ij  metres  (4  feet)  above 
highest  water  level.  The  slopes  exposed  to  wave  action  on  the 
side  of  the  prevailing  wind  are,  in  the  completely  remodelled 
banks,  protected  by  dry  rubble  pitching  to  heights  varying  with 
the  intensity  of  the  wave  action ;  or  else  by  a  dwarf  masonry 
wall  where  the  action  is  too  severe  for  dry  rubble  to  resist.  In 
the  case  of  banks  exposed  to  water  on  one  side  only,  the 
unexposed  slope  is  made  with  a  base  of  ij  to  a  rise  of  i. 


BASIN    IRRIGATION.  25 

The  crest  width  of  the  less  important  banks  of  small  height 
varies  between  3  and  4  metres  (10  and  13  feet),  and  the  crest 
level  is  a  few  inches  lower,  with  reference  to  the  high  water 
level,  than  in  the  case  of  the  more  important  banks. 

In  India,  the  area  of  cultivation  dependent  on  inundation 
canals,  maintained  by  Government,  is  about  4,000,000  acres. 
There  is,  in  addition,  land  irrigated  by  canals  belonging  to  private 
owners,  and  by  other  canals  belonging  to  a  native  State. 

The  chief  inundation  canals  of  India  are  to  be  found  in  the 
basin  of  the  Indus  and  its  five  tributaries.  The  almost  rainless 
district  of  Multan  is  rendered  abundantly  fertile  by  a  series  of 
inundation  canals  fed  by  the  Sutlej  and  the  Chenab  on  either 
side  of  it.  Sind,  also  nearly  rainless,  raises  crops  of  over 
1,500,000  to  2,000,000  acres  by  means  of  the  irrigation  provided 
by  6,000  miles  of  inundation  canals.  In  one  respect  the  inun- 
dation canals  of  the  Punjab  in  India  differ  widely  from  those  of 
Egypt.  The  latter  have  a  bed  slope  of  auuuu  '>  while  the  canals 
of  the  Punjab  have  sometimes  as  steep  a  gradient  as  ^QU*  and 
rarely  less  than  Toioo-  This  difference  is  due  to  the  fact  that 
the  slope  of  the  country  is  much  steeper  in  the  Punjab  than  it 
is  in  Egypt.  Consequently  the  flood  water  of  the  Punjab  rivers 
can  be  brought  to  soil  surface  after  a  much  shorter  run  in  the 
canal  than  is  possible  in  Egypt. 

There  is  one  other  respect  in  which  the  inundation  system  of 
India  differs  from  that  of  Egypt.  In  Sind  and  the  Punjab  in 
India  a  large  proportion  of  the  work  done  by  the  inundation 
canals  is  in  the  irrigation  of  the  kharif  crops — jowar,  bajra  and 
rice.  These  crops  are  irrigated  during  the  flood  season  by  the 
inundation  canals  in  the  ordinary  way,  that  is,  by  field  channels 
fed  "  free-flow  "  from  the  canals,  as  distinguished  from  a  system 
of  inundation.  But  for  the  rabi,  or  cold  weather  crop  of  wheat 
(chiefly),  the  fallow  land  is  inundated  by  the  flood  water  with 
the  same  object  as  in  Egypt,  namely,  to  manure  the  surface  of 
the  ground  with  a  layer  of  silt  deposit,  and  to  saturate  it 


25  IRRIGATION. 

sufficiently  for  the  needs  of  the  winter  crop.  In  Sind  the  rabi 
area  so  inundated  bears  only  a  small  proportion  to  the  whole 
area  irrigated  from  the  inundation  canals;  whereas  in  Egypt 
almost  the  whole  of  the  flood  irrigation  consists  of  the  inun- 
dation preparatory  to  the  sowing  of  the  winter  crops — wheat, 
beans  and  clover.  There  is  a  comparatively  small  area  of 
millet,  raised  by  flow  from  the  flood  canals  of  Egypt,  which 
corresponds  to  the  flood  irrigation  of  kharzf  crops  in  India.  It 
would,  therefore,  seem  more  correct  to  call  such  canals  in  India 
flood  canals;  inasmuch  as  they  irrigate  in  the  ordinary  way 
during  the  flood,  and  inundate  to  a  less  extent ;  whereas  the 
basin  canals  of  Egypt  are  true  inundation  canals,  as  the 
ordinary  irrigation  of  millet  done  by  them  is  insignificant  in 
amount  in  comparison  with  that  effected  by  inundation. 
There  is  no  basin  system  in  India,  properly  so  called,  such  as 
there  is  in  Egypt.  The  inundation  canals  of  India  work 
independently  of  one  another,  without  connection  or  over- 
lapping of  spheres  of  influence,  so  that  there  is  no  opportunity 
afforded  for  correcting  the  shortcomings  of  a  low  flood  by 
leading  water  from  a  higher  system  into  a  lower  one. 

It  is  interesting  to  find  that  the  principle  of  the  basin  system 
of  Egypt  has  been  adopted  by  the  farmers  of  the  North 
Western  Plateau  of  Cape  Colony  in  South  Africa.  Their 
practice  is  thus  described  in  a  report  written  by  Mr.  W.  B. 
Gordon  as  Director  of  Irrigation  of  Cape  Colony. 

"  The  most  successful  works  in  this  tract  are  undoubtedly 
those  which  have  been  constructed  by  the  farmers  themselves, 
for  the  utilisation  of  the  intermittent  flood  waters  on  the 
flat  lands  or  '  vleis '  adjoining  the  rivers,  more  especially  the 
Zak  river,  along  which  these  vleis  are  especially  numerous. 
The  water  is  diverted  from  the  river  by  means  of  a  cheap 
masonry  weir,  or,  where  rock  is  not  available,  by  means  of 
an  earthen  dam  constructed  bank-high  across  the  river  and 
washed  away  by  every  moderate  flood.  Sluit  channels,  or 


BASIN    IRRIGATION.  27 

'  furrows '  as  they  are  called,  convey  the  water  on  to  the  lands 
where  it  is  held  up  to  a  maximum  depth  of  three  to  five  feet  by 
small  banks  or  '  saai '  (i.e.  sowing)  dams  constructed  across  the 
vlei.  When  the  sowing  time  arrives,  the  impounded  water  is 
let  off  to  moisten  the  lands  below  the  dam,  and  these,  together 
with  the  saturated  lands  above,  are  then  ploughed  and  sown." 


CHAPTER   III. 


UNDER  the  basin  system,  described  in  the  last  chapter,  only 
one  crop  can  be  raised  during  the  year,  and  that  only  a  winter 
crop  of  cereals  or  beans.  The  more  valuable  summer  crops 
cannot  be  grown.  These  latter  require  periodical  waterings 
when  the  river  is  low,  and  protection  from  inundation  when 
the  river  is  high.  The  system  of  irrigation  under  which  such 
crops  can  be  matured  is  known  as  "perennial,"  the  water 
supply  being  continuous  throughout  the  year.  When  such  a 
supply  is  obtainable  for  irrigation,  an  average  of  two  crops  a 
year  can  be  grown,  provided  that  the  water  carries  fertilising 
matter  to  the  fields  or  manure  is  freely  used.  The  mean 
value  of  a  perennially  irrigated  crop  is  greater  than  the 
value  of  a  single  basin  crop  of  wheat  or  beans.  Hence 
it  follows  that,  as  two  crops  a  year  are  raised  under  the 
perennial  system  and  only  one  under  the  basin  system,  the 
value  of  the  crops  in  the  former  case  is  more  than  double 
that  in  the  latter,  which  accounts  for  the  fact  that  both  the 
selling  and  renting  value  of  perennially  irrigated  land  is  more 
than  double  that  of  basin  land.  The  preference  for  perennial 
irrigation,  wherever  it  is  possible,  is,  therefore,  quite  natural. 
One  of  the  results  of  the  building  of  the  Assuan  dam  on  the 
Nile,  and  of  the  storage  of  water  above  it  for  use  in  the  summer 
months,  has  been  the  conversion  of  450,000  acres  of  basin  land 
into  land  under  perennial  irrigation.  This  is  the  most  modern 
instance  of  the  development  of  perennial  irrigation  at  the 
expense  of  the  flood  system. 

The  earliest  definite  record  of  perennial  irrigation  has  already 
been  given  in  the  first  chapter.  Hammurabi,  who  ruled  in 
Babylonia  about  four  thousand  years  ago,  must  be  accepted  as 


PERENNIAL   IRRIGATION    AND   WATER   "  DUTY.'  29 

the  oldest  known  constructor  of  perennial  canals.  But,  though 
it  has  been  assumed  that  Egypt  under  the  Pharaohs  owed 
her  prosperity  to  the  basin  system  of  irrigation,  and  that 
perennial  irrigation  was  not  introduced  into  Egypt  till  quite 
recently,  in  Mehemet  Ali's  time,  it  is  by  no  means  improbable 
that  the  extreme  north  of  the  Delta  enjoyed  perennial  irrigation 
in  Ptolemaic  and  Roman  times,  and  had  enjoyed  it  possibly 
for  centuries  before  Hammurabi  dug  his  Grand  Canal  of 
Babylon.  For,  two  thousand  years  ago,  there  was  still  in 
working  order  a  remarkable  natural  reservoir  in  connection  with 
the  Nile,  known  as  Lake  Moeris.  According  to  Herodotus,  who 
visited  the  lake  about  454  B.C.,  the  Nile  water  flowed  into  it  half 
the  year,  and  flowed  back  again  to  the  river  during  the  other 
half.  Strabo  and  Diodorus  Siculus  both  state  that  the  reservoir 
was  still  in  action  nearly  five  hundred  years  later.  Somehow, 
and  at  some  time  since  then,  Lake  Mceris  disappeared,  but  the 
cultivated  lands  of  the  modern  province  of  the  Fayum  have 
been  identified  as  the  bed  of  the  ancient  lake,  and  the  low- 
lying  Lake  Kurun  as  the  persistent  rudiment  of  the  reservoir. 
The  existence  of  such  a  reservoir  as  Herodotus  describes  would, 
it  is  reasonable  to  suppose,  have  created  conditions  of  flow  in 
the  deltaic  branches  of  the  river  favourable  to  the  working  of  a 
system  of  perennial  irrigation  in  the  lowlands  of  the  north 
bordering  the  Mediterranean,  provided  only  that  the  land  level 
had  been  in  those  days  higher  than  it  is  now  with  reference  to 
sea  level ;  and  convincing  evidence  exists  that  it  was  so. 
There  is  also  evidence  to  show  that  this  land,  now  a  barren 
plain,  was  cultivated  in  the  past  and  densely  populated. 
Numerous  mounds  strewn  with  bricks  and  pottery  mark  the 
sites  of  former  towns  and  villages,  and  Rameses  the  Great  and 
ether  Pharaohs  held  their  courts  on  the  Tanitic  branch  of  the 
Nile  at  Zoan,  or  Tanis  (now  San-el-Hagar,  a  fishing  village  of 
the  waste). 

In  India,  the  Madras  native  engineers  introduced  the  system 
of  perennial  irrigation  long  before  the  East   India   Company 


30  IRRIGATION. 

was  formed.  A  weir  across  the  Cauvery  river  in  Madras,  which 
is  called  the  Grand  Anicut,  is  said  to  have  been  constructed 
one  thousand  six  hundred  years  ago — a  modern  work  compared 
to  the  canal  of  Hammurabi  and  Lake  Moeris,  but  still  ancient 
enough  to  discourage  the  present  generation  from  claiming 
perennial  irrigation  as  a  modern  innovation ;  though  it  is 
modern  in  this  sense,  that  it  is  the  system  which  is  now 
adopted  in  all  new  irrigation  projects. 

With  reference  to  this  point,  Mr.  Elwood  Mead,1  in  his 
paper,  already  quoted,  remarks:  "Although  modern  irrigation 
in  the  United  States  only  dates  back  fifty  years,  its  practice  on 
this  continent  is  older  than  historical  records.  The  first 
Spanish  explorers  on  the  Rio  Grande  found  the  Indians  of  that 
valley  watering  the  thirsty  soil,  as  their  forefathers  had  done 
for  unnumbered  generations  before  them,  and  as  their  descen- 
dants are  doing  to-day.  In  Southern  Colorado  and  Northern 
Arizona  and  New  Mexico  are  well-defined  remains  of  irrigation 
works,  of  whose  origin  even  tradition  is  silent." 

With  this  much  of  historical  introduction,  attention  will  now 
be  directed  to  the  study  of  the  methods  of  perennial  irrigation. 
There  are  three  periods  into  which  the  evolution  of  a  canal 
scheme  may  be  divided,  namely :  the  drawing  up  of  the  project, 
the  construction  of  the  works,  and  the  utilisation  of  the  works 
for  the  purpose  for  which  they  are  constructed.  These  subjects 
will  be  taken  in  order,  and  the  various  points  connected  with 
each  considered. 

The  project  has  naturally  to  be  prepared  first.  Suppose, 
then,  that  for  the  sake  of  preventing  famine  or  scarcity,  or  of 
promoting  the  prosperity  of  a  country,  it  has  been  decided  to 
resort  to  irrigation,  and  that  the  irrigation  engineer  has  been 
called  upon  to  prepare  a  project.  He  will  first  of  all  study  the 
climatic  conditions  of  the  country  to  be  irrigated,  and  the 
existing  nature  of  its  agriculture ;  he  will  then  examine  the  soil 

1  Paper  No.  33,  "  Irrigation  in  the  United  States,"  by  Elwood  Mead, 
International  Engineering  Congress  (1904). 


PERENNIAL   IRRIGATION   AND   WATER   "  DUTY."  31 

to  determine  what  crops  it  is  capable  of  bearing  under  the 
stimulus  of  artificial  irrigation,  and  he  will  make  himself 
acquainted  with  the  configuration  of  the  land,  so  as  to  form  a 
general  idea  of  the  scheme  of  canals  and  drains  to  be  elaborated 
afterwards. 

The  rainfall,  as  one  of  the  climatic  conditions  to  be  studied 
at  this  preliminary  stage,  is  that  of  the  region  which  is  to  be 
irrigated,  and  not  of  the  catchment  area  from  which  the  water 
supply  for  the  irrigation  is  to  be  derived.  This  latter  will  form 
the  subject  of  later  study,  when  it  becomes  necessary  to  con- 
sider the  available  sources  of  water  supply.  What  the  engineer 
entrusted  with  the  preparation  of  the  project  first  requires 
to  know  is,  when  and  in  what  quantity  rain  falls  on  the  area  to 
be  cultivated,  with  the  view  of  ascertaining  to  what  extent  the 
rainfall  requires  supplementing  by  irrigation.  And  it  is  not 
only  the  deficiency  of  the  rainfall  that  must  be  taken  note  of, 
but  also  its  capriciousness ;  for  it  is  when  the  climatic  con- 
ditions affecting  agriculture  are  at  their  worst  that  irrigation 
should  prove  itself  a  reliable  insurance  against  loss  of  crops. 
Rainfall  statistics,  so  far  as  they  exist,  must  therefore  be 
collected.  Statistics  of  temperature  are  also  necessary,  as 
temperature  is  a  factor  regulating  the  intensity  of  the  demand 
for  water  and  affecting  the  available  supply  through  evapora- 
tion. The  quality  of  the  soil  is  another  factor  of  similar 
influence :  light  sandy  soils  require  more  water  than  heavy  or 
clay  soils,  and  the  loss  of  water  by  absorption  is  greater  with 
the  former  than  the  latter. 

There  is  an  important  matter  affecting  the  calculations  to  be 
made  that  should  receive  attention  from  the  very  first,  as  a 
preliminary  step.  If  the  source  of  supply  is  to  be  a  river,  and 
reliable  records  of  its  rise  and  fall  and  discharges  do  not  exist, 
gauges  should  be  at  once  set  up  and  regular  readings  taken, 
while  the  discharges  of  the  river  should  be  measured  at  regular 
intervals,  and  the  observations  continued  during  the  period  of 
study,  to  furnish  data,  if  no  better  exist,  upon  which  calculations 


32  IRRIGATION. 

can  be  based.  The  same  should  be  done  if  the  source  is  a  lake : 
its  levels  should  be  regularly  observed,  and  the  discharge  of  its 
in-flow,  or  outlet  channel,  or  both,  regularly  measured. 

The  preliminary  studies  indicated  in  the  foregoing  remarks 
relate  to  the  demand  for  water.  Their  purpose  is  to  furnish 
data  upon  which  to  base  an  estimate  of  the  quantity  of  water 
required  for  the  irrigation  of  the  total  area  to  be  brought  under 
cultivation.  To  make  this  estimate,  we  must  determine  the 
"duty"  of  water  under  the  conditions  of  climate,  soil,  crops, 
and  methods  of  distribution  which  exist,  or  will  exist,  in  the 
tract  to  be  irrigated.  ^ 

The  "  duty  "  of  water  is  a  technical  term  used  by  irrigation 
engineers  to  signify  sometimes  the  amount  of  work  that  water 
may  be  expected  or  ought  to  do  in  irrigating  crops,  and  some- 
times the  amount  it  actually  does  in  any  one  season.  As  the 
word  "  duty  "  implies  an  obligation,  the  former  signification 
would  appear  to  be  the  more  correct,  and  will  be  adopted  in 
this  work.  The  "  duty  "  of  water  may  then  be  defined  as  the 
measure  of  the  efficient  irrigation  work  that  water  can  perform, 
expressed  in  terms  establishing  the  relation  between  the  area 
of  crop  brought  to  maturity  and  the  quantity  of  water  used  in 
its  irrigation.  The  expression  "  efficient  irrigation  work  "  implies 
that  the  water  supplied  to  the  crop  is  neither  more  nor  less 
than  what  is  best  for  it. 

The  relation  between  water  and  crop  can  be  stated  in  various 
ways  according  to  the  unit  of  measure  selected.  The  "  duty  " 
may  be  represented  as  the  area  of  crop  matured  by  a  given 
quantity  of  water  flowing  continuously ;  or  as  the  quantity  of 
continuous  flow  required  to  mature  a  given  area  of  crop ;  or 
as  the  total  volume  required  for  a  given  area  of  crop. 

In  India  the  measure  of  the  "  duty  "  is  expressed  in  terms  of 
that  area  of  crop  which  a  discharge  of  i  cubic  foot  per  second 
(abbrev.  i  cusec),  flowing  continuously  during  the  life  of  the, 
crop,  is  able  to  bring  to  maturity.  This  same  form  of  expres- 
sion is  also  used  in  America  when  considering  the  flow  of  a 


PERENNIAL   IRRIGATION   AND   WATER  "  DUTY."  33 

stream,  with,  however,  "  second-foot "  as  the  abbreviation 
for  i  cubic  foot  a  second.  But  when  the  contents  of  a  storage 
reservoir,  for  instance,  is  in  question,  the  "duty"  of  water  is 
sometimes  expressed  in  terms  of  the  volume  of  water  which 
will  cover  an  acre  to  a  depth  of  i  foot,  and  which,  therefore, 
equals  43,560  cubic  feet.  This  unit  of  volume  is  called  an  "acre- 
foot."  The  storage  capacity  of  a  reservoir  is  given  in  America 
as  so  many  "  acre-feet,"  whereas  in  India  the  content  would 
be  given  as  so  many  million  cubic  feet,  and  in  Egypt  as  so 
many  million  cubic  metres.  The  "  acre-foot "  unit  has  this 
advantage  among  some  others,  that  it  bears  a  direct  relation  to 
the  unit  used  in  defining  areas  of  cultivation,  and  it  is  more 
convenient  for  comparison  with  rainfall  figures  which  are  given 
in  inches  of  depth.  It  is  also  more  suitable  than  cubic  feet 
when  large  volumes  have  to  be  represented  by  figures,  as,  for 
instance,  when  considering  such  matters  as  the  annual  storage 
of  the  Great  Lakes  of  the  St.  Lawrence  basin,  which  is 
calculated  to  reach  a  figure  of  2,419,000,000,000  cubic  feet. 

The  relation  between  the  two  terms — i  cubic  foot  per 
second  (cusec,  or  second-foot)  and  i  acre-foot — is  as  follows : — 
One  cubic  foot  per  second  flowing  for  twenty-four  hours  will 
cover  an  acre  nearly  2  feet  (1*98)  deep ;  that  is,  it  delivers  an 
amount  equal  to  nearly  2  acre-feet.  If  the  acre-foot  is  used  as 
the  term  of  expression,  the  "  duty  "  is  that  number  of  acre-feet 
required  to  mature  an  acre  of  crop. 

In  Southern  Europe  the  "  duty"  is  stated  as  so  many  litres,  or 
sometimes  cubic  metres,  per  second  per  hectare.  In  Egypt  the 
"duty"  is  similarly  expressed  in  terms  of  a  continuous  flow, 
namely,  as  that  discharge  in  cubic  metres  per  day  of  twenty- 
four  hours,  flowing  continuously  during  the  life  of  the  crop, 
which  is  required  per  acre.  It  is  also  sometimes  expressed  in 
the  form  used  in  India,  with  cubic  metres  substituted  for 
cubic  feet,  the  "  duty  "  then  being  the  number  of  acres  of  crop 
which  i  cubic  metre  per  second,  flowing  continuously 
during  the  life  of  the  crop,  can  bring  to  maturity. 

I.  0 


34  IRRIGATION, 

There  is  yet  another  unit  of  quantity  used  in  the  United  States 
West,  known  as  the  "miner's  inch."  It  is  a  little  uncertain  in 
value,  as  it  varies  according  to  the  method  of  measurement.  In 
California  it  represents  a  fiftieth  part  of  a  second-foot,  in 
Arizona  a  fortieth. 

The  "  duty "  of  water  is  said  to  be  a  high  or  a  low  one 
according  as  a  given  quantity  successfully  irrigates  a  large  or  a 
small  area. 

The  different  methods  of  expressing  the  "duty"  of  water 
have  each  points  to  recommend  them,  according  to  the  object 
of  the  calculation  in  which  the  "  duty"  forms  one  of  the  factors. 
Thus,  if  it  is  desired  to  determine  the  area  of  crop  that  a 
known  discharge  can  irrigate,  it  is  convenient  to  have  the 
"duty"  expressed  as  the  area  that  a  continuous  discharge  of 
i  cubic  foot,  or  i  cubic  metre,  a  second  can  irrigate.  If, 
on  the  other  hand,  the  calculation  of  the  discharge  required  for 
the  irrigation  of  a  given  area  is  being  worked  out,  it  is  more 
convenient  to  have  the  "duty"  expressed  in  the  form  most 
used  in  Egypt,  namely,  as  the  number  of  cubic  metres  required 
to  irrigate  an  acre.  The  acre-foot,  it  has  already  been  pointed 
out,  is  a  convenient  form  to  use  in  calculations  relating  to  large 
storage  works. 

As  the  "  duty  "  of  water,  or  the  measure  of  its  power  of  doing 
work,  is  the  basis  of  all  calculations  in  the  design  of  an  irrigation 
project,  it  may  be  well  to  show  by  a  simple  example  how  the 
"  duty  "  may  be  arrived  at.  Let  it  be  assumed  that  the  conditions 
of  climate  and  soil,  and  of  crop  requirements,  are  such  that 
waterings  are  required  at  intervals  of  eighteen  days,  and  that 
each  watering  is  equal  in  volume  to  the  quantity  represented 
by  a  depth  of  3^  inches  over  the  land  surface.  An  acre  has  a 
superficial  area  of  43,560  square  feet.  Each  watering  will  there- 
fore require  a  quantity  of  (^  X  43,560  =J  12,705  cubic  feet  per 

acre  at  the  field.     If  it  is  desired  to  calculate  the  "duty "of 
water  at  the  canal  head,  so  as  to  determine  what  quantity  the  main 


PERENNIAL  IRRIGATION   AND  WATER   "DUTY."  35 

canal  must  draw  in  from  the  source  of  supply,  an  allowance  must 
be  made  for  loss  of  water  between  the  canal  head  and  the  field. 
What  this  allowance  should  be  depends  upon  many  things. 
The  loss  is  rarely  less  than  30  per  cent.,  and  may  even  amount 
to  as  much  as  70  per  cent,  when  the  conditions  are  unfavourable 
to  economy.  It  is  due  to  evaporation  and  absorption  in  the 
carrying  canals  and  to  waste  in  the  fields.  The  condition  of 
the  canals,  and  the  degree  of  skill  and  care  applied  by  both 
engineers  and  cultivators  to  the  distribution  of  the  water,  has 
great  influence  on  the  amount  of  the  loss.  Evaporation, 
moreover,  varies  with  temperature  and  with  the  humidity  of 
the  atmosphere ;  absorption  with  the  soil ;  and  both  with  the 
distance  that  the  water  has  to  travel  between  the  source  and 
the  crop.  The  calculations  must  therefore  admit  the  inevitable 
coefficient  that  varies  with  the  particular  conditions  of  each 
case,  and  so  introduce  the  element  of  individual  judgment 
which  is  so  liable  to  err.  However,  there  is  no  help  for  it. 

The  percentage  of  loss  by  absorption  is  greater  in  new 
canals  than  in  old  ones  in  consequence  of  the  staunching  action 
of  silt  deposit  both  on  the  bed  and  slopes.  The  absorption 
naturally  bears  a  direct  relation  to  the  extent  of  the  surface  of 
the  bed  and  slopes  with  which  the  water  is  in  contact.  Recog- 
nising this,  the  engineers  of  the  Punjab,  in  India,  use  this  area 
as  the  basis  of  their  estimate  of  the  quantity  absorbed,  assuming 
a  loss  of  8  cubic  feet  a  second  per  million  square  feet  of 
wetted  surface. 

From   experiments   made  on   the   Ganges   and   Bari    Doab 
Canals  in  India,  the  following  conclusions  as  to  the  loss  of 
water   from   evaporation   and    absorption   in   running    canals, 
between  the  source  of  supply  and   the  crop,  were  arrived  at. 
Of  the  volume  drawn  in  at  the  canal  head — 
15  to  20  per  cent,  is  lost  in  the  canal ; 
6  to    7  per  cent.  ,,    „     „    „    distributaries ; 
21  to  22  per  cent.  ,,    „     „    ,,    village  water-courses, 

It  was  further  held  that  half  of  the  remainder  was  wasted  in 

D  2 


30  IRRIGATION. 

various  ways  by  the  cultivators,  mainly  in  excessive  irrigation. 
This  is  evidently  somewhat  of  an  assumption,  and,  in  any  case, 
the  figure  arrived  at  by  actual  experience,  as  that  which 
represents  the  "duty"  of  water,  will  cover  this  waste,  if  waste 
there  is.  It  is  not  reasonable  to  expect  such  economy  on  large 
irrigation  systems  as  is  obtainable  when  each  plant  is  served  by 
a  watering  pot. 

If  the  loss  between  the  canal  head  and  the  crop  is  assumed 
to  amount  to  40  per  cent,  of  the  discharge  entering  the  canal 
head,  the  estimate  of  water  required  is  completed  as  follows, 
it  having  already  been  found  that  the  quantity  required  at  the 
field  for  a  single  watering  of  I  acre  is  12,705  cubic  feet.  If 
Q  is  the  quantity  drawn  in  at  the  head,  its  value  will  then  be 
found  from  the  following  equation 

Q  ~  iHJ)  Q  =  !2,705  cubic  feet: 
whence  Q  =  21,175  cubic  feet. 

This  is  the  quantity  required  per  acre  of  crop  once  every  eight- 
teen  days ;  or,  in  other  words,  a  continuous  discharge  at  the 
canal  head  of  1,175  cubic  feet  per  day  is  required  for  every 
acre  of  crop.  This  is  one  way  of  expressing  the  "  duty." 

There  is  next  to  be  determined  the  value  of  the  "  duty " 
expressed  in  the  area  irrigated  by  i  cubic  foot  a  second.  To 
arrive  at  this,  the  calculation  must  be  made  of  the  number  of 
times  a  discharge  of  i  cubic  foot  a  second,  flowing  for  eighteen 
days,  will  give  the  quantity  required  for  a  single  watering  of 
i  acre,  namely,  21,175  cubic  feet.  A  discharge  of  i  cubic 
foot  a  second  gives  86,400  cubic  feet  a  day,  or  1,555,200 
cubic  feet  in  eighteen  days;  and  is  therefore  sufficient  to 
irrigate 

^555^00  =  acres> 

2i,i75 

Hence,  under  the  conditions  assumed,  73*44  acres  is  the  "  duty" 
of  the  supply  at  the  canal  head. 

The  results  of  actual  experience  will  now  be  given. 

In  India  the  "  duty  "  varies  considerably,  as  might  be  expected 


PERENNIAL  IRRIGATION   AND   WATER  "DUTY."  37 

in  a  country  where  the  conditions  affecting  it  have  so  wide  a 
range  of  variability.  There  are  two  crop  seasons  in  India, 
known  as  the  kharif  and  the  rabi.  The  kharif  season  includes 
the  period  of  heavy  rain,  which  may  be  said  to  extend,  generally, 
from  the  middle  of  June  to  the  middle  of  October ;  the  rabi 
season  is  the  period  of  cold  weather,  November  to  March.  **  The 
crops  of  the  kharif  season  are,  in  the  United  Provinces  and  the 
Punjab,  maize,  indigo,  cotton,  and  other  crops,  with  a  small 
proportion  only  of  rice ;  in  Bengal  they  are  almost  entirely  rice. 
The  crop  of  the  rabi  season  is  mainly  wheat.  As  a  rough 
average  it  may  be  reckoned  that  i  cubic  foot  a  second  will 
irrigate  from  140  to  160  acres  of  rabi  crop,  and  70  to  80  acres 
of  kharif. 

In  Egypt  the  "duty"  has  been  worked  out  carefully  for  the 
summer  crops  only,  of  which  sugar-cane  and  cotton  are  the 
most  important ;  and  it  has  been  assumed  that  rice  (also  a 
summer  crop)  takes  double  the  amount  of  water  that  the  other 
crops  do.  During  the  life  of  these  crops  no  rain  falls,  so  that 
they  are  entirely  dependent  on  the  canals  for  the  water  necessary 
to  their  growth.  As  the  result  of  observations  made  during  a 
succession  of  summers  of  very  low  supply  in  the  Nile,  the 
conclusion  was  arrived  at  that  an  allowance  of  water  at  the  rate 
of  30  cubic  metres  a  day  per  acre  of  summer  crop,  and  double 
that  amount  for  rice,  is  sufficiently  liberal  to  provide  a  watering 
every  eighteen  days  for  cotton,  sugar-cane,  &c.,  and  every  nine 
days  for  rice;  or,  in  other  words,  i  cubic  metre  per  second 
is  sufficient  for  2,880  acres  of  summer  crop,  or  half  that  area  of 
rice.  "This  is  equivalent  to  saying  that  i  cubic  foot  a  second 
will  irrigate  8i|  acres  of  summer  crop,  or  half  that  area  of  rice. 
In  Egypt  it  has  been  found  that  40  per  cent,  of  the  gross  area 
is  annually  put  under  summer  crop.1  The  "  duty"  above  stated, 
of  30  cubic  metres  a  day,  is  per  acre  of  crop;  if  this  is  converted 
into  the  "duty"  per  acre  of  gross  area,  the  figure  becomes  12 
cubic  metres.  If,  then,  the  area  commanded  by  a  canal 

1  See  Note  4,  Appendix  IV. 


38  IRRIGATION. 

system— which  in  Egypt  is  identical  with  the  gross  area— is 
e.g.,  1,000,000  acres,  the  discharge  required  to  be  drawn  into  the 
main  canal  from  the  source  of  supply  is  12,000,000  cubic  metres 
a  day  during  the  life  of  the  summer  crops.1 

In  the  perennially  irrigated  tracts  of  Egypt  it  is  reckoned  that 
nearly  all  the  land  is  under  crop  during  the  flood  season,  40  per 
cent,  being  cotton  and  the  remainder  maize.  For  the  flood 
season  an  allowance  of  25  cubic  metres  a  day  per  acre  of  gross 
area  is  the  accepted  figure.  The  levels  obtainable  in  the  flood 
season  being  higher  than  at  other  times,  the  increased  discharge 
can  easily  be  supplied.  By  a  system  of  distribution  that  is 
favourable  to  agriculture  both  in  the  flood  and  summer  season 
(to  be  described  later)  the  canals  are  made  to  carry  the  summer 
and  flood  discharges  with  convenient  surface  levels,  though  one 
is  nearly  double  the  other  in  volume. 

As  regards  the  rice  crop  in  India,  irrigation  engineers  have 
practically  accepted  50  acres  at  the  head  of  the  canal  system  as 
the  "duty"  for  a  continuous  discharge  of  i  cubic  foot  a 
second,  allowing  a  period  of  about  twelve  days  for  irrigating 
the  whole  area  of  crop.  In  Eygpt,  when  the  intervals  between 
waterings  are  fixed  at  nine  days,  the  duty  is  42  acres  for  the 
same  discharge.  If  this  latter  period  were  to  be  extended  to 
eleven  days,  the  "  duty "  would  rise  to  51  acres.  As  the 
period  in  India  is  given  as  about  twelve  days,  it  may  be  said 
that  both  India  and  Egypt  are  agreed  upon  this  point. 

It  is  interesting  to  find  that  the  recent  experience  of  irrigation 
in  India  and  Egypt  has  led  to  the  same  conclusion  as  that 
reached  by  Italian  engineers  fifty  years  ago.  It  has  been  stated 
above  that  in  Egypt  i  cubic  foot  a  second  will  irrigate  8i£ 
acres  of  summer  crop,  or  half  that  area,  say  42  acres,  of  rice. 
Now  Baird  Smith,  in  "  Italian  Irrigation,"  1855,  Vol.  II.  p.  66, 
states  that,  "  According  to  the  best  Italian  authorities,  i  cubic 
foot  per  second  is  sufficient  for  the  irrigation  of  from  35  to  40 

1  In  this  calculation  the  extra  allowance  for  the  comparatively  small  area 
of  rice  has  not  been  taken  into  account. 


PERENNIAL  IRRIGATION   AND  WATER  "DUTY."  39 

acres  of  rice";  and  adds,  "  This  is  fully  twice  the  quantity 
required  for  ordinary  meadow  irrigation."  He  also,  when 
summing  up,  comes  to  the  conclusion  that,  "  under  ordinary 
circumstances,  the  effective  power  per  cubic  foot  per  second  is 
93  acres." 

Sir  Colin  Scott-Moncrieff,  in  his  "  Irrigation  in  Southern 
Europe,"  1868,  presents  a  Table  on  p.  33  which  gives,  for  the 
south  of  France,  a  mean  "  duty  "  of  83*4  acres,  watered  during 
the  six  months  of  irrigation,  for  a  continuous  discharge  of 
i  cubic  foot  per  second,  with  seven  to  fifteen  day  intervals 
between  waterings. 

Wilson,  in  his  "  Irrigation  Engineering,"  1903,  gives  the 
following  information  concerning  "  duties "  in  the  United 
States: — "The  State  engineer  of  Colorado  now  accepts  100 
acres  per  second-foot  as  the  "  duty "  for  that  State,  varying 
on  the  supply  at  the  head  from  70  to  190  acres.  In  Utah  70 
to  300  acres  per  second-foot  is  the  duty.  In  Montana  it  is 
about  80  acres  per  second-foot." 

In  Southern  California  the  "duty"  obtained  is  very  high. 
For  surface  irrigation  it  is  150  to  300  acres ;  for  sub-irrigation 
from  pipes  300  to  500  acres.  So  high  a  "duty"  is  only  to  be 
obtained  by  the  use  of  cemented  channels  and  pipes  for  carrying 
the  water,  and  probably  only  in  the  case  of  orchard  cultivation. 

Newell,  in  "  Irrigation,"  1902,  p.  214,  states:  "  It  is  frequently 
estimated  that  i  cubic  foot  per  second,  or  second-foot  flowing 
through  an  irrigating  season  of  ninety  days,  will  irrigate  100 
acres."  This,  as  a  rule  of  thumb,  would  be  a  convenient  one, 
but,  in  the  case  of  kharif  in  India  and  summer  crops  in  Egypt, 
70  to  80  acres  would  seem  to  more  accurately  represent  the 
average  "duty." 

In  a  report  on  the  best  method  of  utilising  in  irrigation  the 
waters  of  the  River  Guadalquivir,  made  in  1906  by  Mr. 
R.  B.  Buckley  and  the  author  of  this  work  for  the  Spanish 
Government,  the  "  duty  "  adopted  in  the  projects  recommended 
was  i  cubic  metre  per  second  for  every  2,000  hectares  of  winter 


40  IRRIGATION. 

crop,  and  for  every  1,000  hectares  of  summer  crop.  This  is 
equivalent  to  a  "  duty  "  of  140  acres  in  winter  and  70  acres  in 
summer  for  each  cubic  foot  of  discharge  per  second.  In  the 
same  report  the  duration  of  the  irrigating  seasons  was  reckoned 
as  six  months  for  the  winter  crop  and  four  months  for  the 
summer  crop. 

When  the  engineer  entrusted  with  the  preparation  of  a 
project  has,  after  consideration  of  all  the  conditions  affecting 
the  question,  decided  on  the  "  duty"  for  each  crop  or  season, 
and  has  ascertained  the  areas  under  crop  in  the  different 
seasons,  and  the  periods  for  which  each  crop  requires  irrigation, 
it  is  then  a  simple  matter  to  calculate  with  these  data  the 
discharges  required  throughout  the  year,  or  the  quantity  of 
water  that  it  is  necessary  to  store  annually.  If  it  is  the  con- 
tinuous discharge  of  a  canal  which  it  is  desired  to  determine, 
the  duration  of  the  life  of  the  crop  does  not  affect  the  calculation. 
If,  for  example,  the  "  duty  "  for  a  particular  crop  or  season  is 
80  acres  per  cubic  foot  of  discharge  per  second,  the  discharge 

required  for  10,000  acres  of  crop  will  be(  — ^ —  =  j  125  cubic 

feet  a  second  flowing  continuously  for  the  period  during  which 
the  crop  requires  irrigation,  whatever  that  period  may  be.  If, 
on  the  other  hand,  it  is  desired  to  calculate  the  total  volume 
of  water  required  to  bring  a  crop  to  maturity,  as  may  be 
necessary  in  considering  the  question  of  storage,  the  period  of 
flow  is  a  necessary  factor.  In  India  this  period  is  technically 
known  as  the  base  of  the  "  duty."  Taking  the  same  example 
as  before,  if  the  "  duty  "  is  80  acres  per  cubic  foot  per  second, 
and  the  area  of  crop  10,000  acres,  and  the  time  during  which  it 
requires  irrigation  one  hundred  days,  the  total  volume  required  to 

mature  the  crop  will  be  f     '    -  X  86,400  X  100=  j  1,080,000,000 

cubic  feet.  In  this  case  the  "  duty "  of  the  water  of  the 
reservoir  may  be  expressed  as  108,000  cubic  feet  per  acre, 


PERENNIAL  IRRIGATION    AND   WATER  "DUTY.*  4! 

implying  that,  on  the  average,  each  volume  of  108,000  cubic 
feet  of  water  drawn  from  the  reservoir  is  sufficient  to  mature 
i  acre  of  crop.  An  addition  to  the  total  volume  required  to 
mature  the  crop  must  be  made  to  allow  for  evaporation  and 
absorption  in  the  reservoir  itself,  in  order  to  arrive  at  the  total 
quantity  of  storage  necessary.  In  this  example  it  is  assumed, 
in  the  first  case,  that  the  "  duty  "  used  is  that  at  the  head  of 
the  canal,  and  in  the  second  case  at  the  reservoir  outlet. 

The  amount  of  irrigation  work  that  canal  water  actually 
does — or,  rather,  is  shown  in  annual  reports  as  doing — varies 
from  year  to  year  in  consequence  of  the  rainfall  not  being  a 
constant  quantity.  The  explanation  of  this  is  that  the  canal 
water  is  credited  with  the  work  done  by  the  rain.  This 
accounts  for  the  great  variation  in  the  so-called  "duty" 
(signifying  work  actually  done)  which  appears  in  the  annual 
irrigation  reports  of  India  for  any  particular  canal.  Taking, 
for  example,  the  November  figures  of  the  Bari  Doab  Canal  for 
ten  years,  the  "  duty  "  (work  actually  done)  of  i  cubic  foot 
a  second  varies  from  in  to  222  acres,  the  average  being 
169  acres.  From  the  statistics  of  work  actually  done  by  water, 
the  amount  of  work  which  it  may  be  expected  to  do,  under 
either  normal  or  extreme  conditions  as  may  be  desired,  is 
determined.  In  the  particular  case  of  the  Bari  Doab  Canal, 
the  accepted  "  duty  "  for  the  rabi  season,  representing  the 
work  that  ought  to  be  done,  is  160  acres  to  the  cubic  foot  per 
second.  The  statistics  of  the  month  of  November  were 
selected  for  ascertaining  the  "  duty,"  as  November  is  the 
month  in  which  the  rabi  sowings  are  principally  made,  and 
the  "  duty "  which  can  be  obtained  in  that  month  may 
determine  the  area  of  crop  which  can  be  sown. 

Mr.  Buckley  points  out  that  it  is  the  "  duty  "  of  the  "  period 
of  pressure,"  or  greatest  demand,  and  not  of  the  whole 
irrigating  season,  which  is  the  important  "  duty  "  to  determine. 
"  The  '  duty '  of  water  drawn  in  at  the  head  of  a  system  is  a 


42  IRRIGATION. 

useful  factor  in  many  ways,  but  it  is  often  most  desirable  to 
gauge  it  at  other  points  in  the  system,  and  with  reference  to 
different  '  bases,'  that  is,  to  shorter  periods  of  time  than  that 
of  the  whole  irrigating  period  of  a  crop  ;  for  the  'duty '  based  on 
the  discharge  drawn  from  the  source  6f  the  supply  on  the 
average  of  the  whole  season  fails  to  take  cognisance  of 
fluctuating  demands.  It  is  necessary  in  most  cases  to  know 
not  only  the  average  discharge  of  a  season,  but  the  maximum 
discharge  required  at  a  period  of  pressure  during  the  season." 

The  summer  "  duty  "  of  water  in  Egypt  is  not  calculated  from 
the  whole  irrigating  period  of  a  crop,  but  from  the  period 
during  which  the  whole  available  supply  in  the  Nile  is  utilised 
and  it  is  found  necessary  to  apply  rotations  to  secure  a  fair 
distribution  of  water.  The  duration  of  the  latter  period  varies 
from  seventy  to  one  hundred  days.  If  any  longer  period  is 
used  for  the  calculation  of  the  "  duty,"  such,  for  instance,  as 
the  life  of  the  crop,  the  "  duty "  would  appear  less  than  it 
should,  in  consequence  of  surplus  water,  that  was  doing  no 
work,  not  being  eliminated  from  the  calculations. 

Similarly,  when  rain  supplements  artificial  irrigation,  the 
"  duty"  appears  higher  than  it  should  do,  as  the  watering  done 
by  the  rain  is  credited  as  work  done  by  the  canal  water. 


CHAPTER   IV. 

SOURCES   OF   SUPPLY. 

THE  preceding  chapter  deals  with  the  considerations  that 
regulate  the  demand  for  irrigation  water :  the  present  chapter 
relates  to  the  question  of  supply. 

Rainfall  is  the  primary  source  of  all  water  supplies ;  but  if 
rain  does  not  fall  when  or  where  the  need  of  water  is  felt, 
then  artificial  means  must  be  devised  to  keep  it  in  hand  when 
it  does  fall,  till  it  is  wanted,  or  to  carry  it  to  the  place  where  it 
is  required,  unless  Nature  has  undertaken  to  do  both.  Rivers 
are  Nature's  waterways  which  carry  the  rain-water  that  falls 
in  their  catchment  areas  to  regions  where,  may  be,  no  rain 
falls.  The  case  of  the  Nile  and  Egypt  has  already  been  cited 
as  a  well-known  example.  But  the  open  channels  of  rivers  are 
not  the  only  natural  carriers,  though  they  do  by  far  the  heaviest 
part  of  the  work.  Water  travels  also  by  ways  unseen,  in  closed 
channels  underground,  confined  between  watertight  strata,  and 
feeds  springs  and  wells,  often  at  great  distances  from  the  starting- 
point.  Such  a  natural  arrangement  fulfils  both  duties ;  it  not 
only  provides  for  carrying  the  water  to  the  places  where  it  is 
used,  but  for  holding  it  in  reserve  till  it  is  drawn  upon. 

This  underground  supply,  when  utilised  for  irrigation,  is 
tapped  chiefly  by  wells  fitted  up  with  some  form  of  lifting 
apparatus.  From  the  point  of  view  of  agriculturists  well- 
irrigation  is  an  important  matter.  It  has  been  estimated  that, 
of  the  44,000,000  acres  under  irrigation  in  British  India  in  1903, 
13,000,000  acres  were  irrigated  from  wells,  of  which  there  were 
probably  2,500,000. 

In  Egypt  well-irrigation  has  less  importance,  and  will  have 


44  IRRIGATION. 

less  and  less  as  the  canal  system  becomes  more  perfect. 
There  are  some  30,000  wells  still  used  for  irrigation  in  Lower 
and  Upper  Egypt. 

In  California  there  are  about  150,000  acres  served  by  wells,  the 
artesian  conditions  of  the  Californian  valley  being  exceptionally 
favourable  to  this  form  of  irrigation.  There  are  said  to  be 
8,097  artesian  wells  in  the  State. 

Important  though  well-irrigation  may,  therefore,  be  held  to 
be  as  an  aid  to  agriculture,  the  construction  of  wells  and  the 
management  of  the  irrigation  effected  by  them  are  matters 
which  are  not  generally  considered  to  lie  within  the  province 
of  the  irrigation  engineer.  They  have  hitherto  been  left  to 
private  enterprise,  and  the  farmer  would  probably  prefer  to 
have  it  so.  For,  as  Sir  Colin  Scott- Moncrieff  pointed  out  in 
his  Address  to  the  Engineering  Section  of  the  British  Associa- 
tion, 1905,  "  there  is  one  practical  advantage  in  irrigating  with 
the  water  raised  from  one's  own  well,  or  from  a  river — it  is  in 
the  farmer's  own  hands.  He  can  work  his  pump  and  flood  his 
lands  when  he  thinks  best.  He  is  independent  of  his  neigh- 
bours, and  can  have  no  disputes  with  them  as  to  when  he  may 
be  able  to  get  water  and  when  it  may  be  denied  to  him."  But, 
though  well-irrigation  can  be  made  a  profitable  farming  opera- 
tion for  any  class  of  crop  when  carried  out  by  cultivators 
who  work  on  the  land  themselves  and  use  their  own  cattle,  it  is 
otherwise  an  expensive  method,  and  can  only  be  made  to  pay 
by  cultivating  the  more  valuable  kinds  of  crops.  Moreover,  it 
would  seem  to  be  out  of  favour  with  those  who  have  had  experience 
of  both  canal  and  well  water  Mr.  Buckley  remarks  :  "  The 
superiority  of  the  rain-water  over  that  of  wells  is  demonstrated  by 
the  fact  that  near  the  heads  of  the  Punjab  canals  the  cultivators 
prefer  to  pay  canal  rates  and  to  lift  the  water  from  the  canals 
rather  than  to  lift  it  from  wells,  although  the  canal  level  and 
the  spring  level  are  about  the  same."  On  the  other  hand, 
during  the  cold  weather,  well  water  is  given  the  preference  on 
account  of  its  higher  temperature  as  compared  with  canal 


SOURCES  OF  SUPPLY.  45 

water.  To  this  day  the  opium  cultivators  of  Behar,  a  district 
of  India,  lift  water  from  their  wells  rather  than  run  it  on  to 
their  fields  from  the  canals. 

Rivers  are  the  principal  sources  from  which  the  irrigation 
engineer  draws  the  supply  of  water  required  to  feed  a  canal 
system.  Some  rivers  are  fed  by  rain,  others  by  snow.  If  they 
are  fed  by  rain,  the  rise  and  fall  of  the  river  will  respond  to  the 
rainfall  more  or  less  faithfully  according  to  the  remoteness  and 
nature  of  the  catchment  area  in  which  the  rain  falls,  if  no  lakes 
intervene  to  affect  the  forward  flow.  If  the  rivers  are  fed  by 
snow  falling  on  mountain  heights  where  their  sources  lie,  the 
rise  of  the  river  will  commence  when  the  summer  heat  causes 
the  snow  to  melt.  The  snowfields  that  feed  certain  rivers 
are  Nature's  reservoirs  for  the  storage  of  water  till  the 
summer  comes.  And,  moreover,  such  reservoirs  are  automatic 
in  their  action,  for,  the  greater  the  heat,  the  greater  will  be  the 
want  of  water  for  irrigation,  and  the  more  plentiful  the 
discharge  from  the  melting  snow.  This  convenient  arrange- 
ment produces  conditions  favourable  to  the  working  of  a 
system  of  perennial  irrigation.  The  Indus  and  other  rivers 
of  Upper  India  are  snow-fed.  So,  also,  is  the  Tigris ;  but, 
though  the  dawn  has  appeared,  Mesopotamia  is  still  waiting 
for  the  rising  of  a  fully  developed  Irrigation  Department  with  a 
mandate  to  take  advantage  of  the  gifts  that  Nature  offers  and 
restore  to  the  land  of  the  twin  rivers  its  former  prosperity. 

There  are  some  rivers  which  have  lakes  for  their  sources,  the 
lake  basins  serving  as  collecting  reservoirs  for  the  rain  which 
falls  in  their  catchment  areas.  Rivers  so  fed  do  not  exhibit  the 
same  fluctuation  of  levels  as  rivers  that  have  no  such  collecting 
basins  to  operate  as  moderators.  The  largest  group  of  natural 
reservoirs  in  the  world  are  the  great  lakes  of  the  St.  Lawrence 
basin  above  the  Niagara  Falls,  which  have  a  surface  area  aggre- 
gating nearly  88,000  square  miles,  and  a  catchment  of  265,095 
square  miles.  The  mean  annual  fluctuation  of  the  levels  of 
these  lakes  is  very  nearly  i  foot.  A  layer  of  i  foot  depth 
over  the  lake  area  of  88,000  square  miles  would  contain  2,453 


46  IRRIGATION. 

billion  cubic  feet,  sufficient  to  produce  a  discharge  of  76,500 
cubic  feet  a  second  for  a  year.  In  consequence  of  the  great 
regulating  action  of  these  lakes,  with  their  enormous  storage 
capacity  and  evaporating  surface,  there  is  no  such  thing  as 
high  and  low  water  recognised  on  the  river  below.  The  wealth 
of  water  carried  by  the  St.  Lawrence  river  pursues  its  way  to 
the  Atlantic  through  the  humid  region  where  the  rainfall  is 
copious — usually  from  40  to  60  inches  per  annum,  or  even 
more — so  that  it  is  not  agriculture  that  benefits  by  the  con- 
stancy of  the  river  discharge,  but  navigation  only.  For  in  the 
eastern  half  of  the  United  States  it  is  drainage  and  not 
irrigation  that  requires  attention. 

There  are  in  Europe  also  natural  reservoirs  which  act  with 
similar  effect  to  the  St.  Lawrence  lakes,  but  they  are  on  a  very 
much  smaller  scale.  The  Po  discharge  has  a  constancy  due  to 
the  fact  that  it  is  drawn  from  Lakes  Como,  Maggiore  and 
Garda ;  the  Rhone  is  moderated  by  the  influence  of  Lake 
Geneva,  and  the  Rhine  by  Lakes  Constance  and  Neuchatel, 
The  aggregate  area  of  the  surfaces  of  these  six  lakes  is  less  than 
one  hundredth  part  of  the  area  of  the  St.  Lawrence  lakes  above 
the  Niagara  Falls. 

The  Yenisei  river,  in  Siberia,  is  fed  by  the  Baikal  lake, 
which  has  an  area  of  12,430  square  miles. 

The  equatorial  lakes  of  Africa  are  the  most  worthy  rivals  of 
the  St.  Lawrence  lakes  in  respect  of  the  aggregate  surface  area 
of  the  group,  but  their  influence  is  divided  between  three  rivers. 
There  is  Lake  Nyassa,  of  9,000  square  miles  area,  at  the  source 
of  the  Shire",  a  tributary  of  the  Zambesi ;  there  is  Lake  Tanganyika, 
of  12,650  square  miles,  together  with  smaller  lakes,  at  the  source 
of  the  Congo ;  and  the  Victoria,  Albert  and  Albert  Edward 
Nyanzas,  of  29,000  square  miles  aggregate  area,  at  the  sources 
of  the  White  Nile.  The  Nile  lakes  certainly  exercise  a  moderating 
effect  on  the  fluctuations  of  the  White  Nile,  but,  unfortunately 
for  Egypt  and  the  Sudan,  the  moderating  influence  is  carried 
too  far,  as  the  lakes  not  only  act  as  collecting  and  storage 


SOURCES  OF   SUPPLY.  47 

basins,  but  as  evaporating  tanks  as  well,  with  surfaces  so 
extensive  in  relation  to  their  catchment  areas  that  an  excessive 
proportion  of  the  rainfall  is  lost  by  evaporation.  And  this  loss 
is  increased  to  a  serious  extent  in  the  enormous  swamps  known 
as  the  Sudd  region,  which  the  water  has  to  traverse  on  its  way 
to  the  North.  Evaporation  from  the  water  surface  of  these 
marshes  and  absorption  by  water  plants  reduces  the  discharge  of 
the  river  by  more  than  a  half. 

However  beneficial  as  moderators  of  extremes  of  high  and  low 
discharges  natural  reservoirs  may  be,  it  is  seldom  that  they  act 
conveniently  in  all  respects  without  artificial  control.  In  the 
interests  of  navigation  an  extensive  system  of  artificial  reservoirs 
has  been  constructed  out  of  some  of  the  many  lakes  at  the  sources 
of  the  Mississippi  river.  Another  fine  example  of  such  reservoirs 
exists  in  Russia  at  the  interlacing  sources  of  the  Volga  and  the 
Msta  rivers.  By  the  water  stored  in  these  reservoirs,  which 
comprise  several  lakes,  the  navigability  of  the  two  rivers  is  main- 
tained during  the  season  of  low  water  ;  and,  with  the  help  of  an 
artificial  waterway,  the  Volga  is  connected  with  the  Msta,  and 
thereby  the  Caspian  with  the  Baltic. 

But  instances  of  natural  lakes  under  artificial  control  serving 
rivers  on  which  irrigation  systems  depend  are  rare.  One  such 
instance  there  is  on  record,  but  the  lake  as  an  effective  reservoir 
is  now  extinct.  Mention  has  already  been  made  of  Lake  Moeris 
as  described  by  Herodotus.  He  was  told  by  his  guide  that  the 
lake  was  an  artificial  one,  and  it  seems  that  he  believed  it.  But 
he  need  not  have  done  so,  as  the  guide  had  no  possible  means  of 
knowing  how  the  lake  came  into  being,  several  thousand  years 
before  he  was  born .  There  is  little  doubt  that  the  crops  of  the 
modern  Fayum  Province  are  grown  on  the  bed  of  the  ancient 
lake.  The  lake  would  have  had  a  surface  area  of  about  700 
square  miles,  and  a  superior  layer  of  about  10  to  15  feet  depth  of 
water  which  could  have  been  used  to  supplement  the  river  in 
summer.  It  was  not  situated  at  the  Nile  sources,  but  some 
3,000  miles  below  them,  and  about  60  miles  above  the  apex  of 


48  IRRIGATION. 

the  Delta.  Neither  was  it  in  the  track  of  the  river  itself,  for  it  lay 
just  outside  the  Nile  valley,  but  was  connected  with  the  river  by 
a  short  branch,  like  a  bud  on  its  stalk.  In  this  situation  it  was 
most  conveniently  placed  to  act  as  a  moderator  of  fluctuations 
of  level  in  the  Deltaic  branches  of  the  river.  This  natural  reser- 
voir was  brought  under  control  by  regulators  constructed  on 
the  channels  of  in-flow  and  out-flow,  so  that  the  flood  water 
could  be  admitted  to  the  lake  to  the  extent  desired,  and  the 
stored  water  be  returned  to  the  river  when  it  was  wanted. 
Possibly  this  reservoir  also  was  worked  in  the  interests  of 
navigation  only,  but,  as  has  been  already  suggested,  it  may  have 
also  promoted  the  former  prosperity  of  the  northern  margin  ot 
the  Delta  by  providing  a  sufficient  supply  of  water  for  cultiva- 
tion at  other  seasons  of  the  year  than  that  of  flood. 

The  Lake  Mceris  reservoir  was  in  a  peculiarly  favourable 
situation  for  moderating  high  floods  and  supplementing  low 
summer  discharges  in  the  Deltaic  branches  of  the  Nile. 
Usually  the  lakes  which  act  as  natural  reservoirs  to  rivers  are 
located  near  their  sources,  at  a  distance,  sometimes  very  great, 
from  the  point  where  any  beneficial  effect  from  their  action 
would  first  be  felt.  One  great  disadvantage  resulting  from  the 
distance  is  that  much  of  the  stored  water  is  lost  by  evaporation 
and  absorption  during  its  flow.  Another  drawback  is  the 
difficulty  of  regulating  the  supply  from  the  reservoir  so  as  to 
give  the  exact  amount  required  at  a  distant  point,  where  the 
effect  of  any  alteration  of  the  reservoir  out-flow  would  not  be 
felt  for  many  days  after. 

In  the  absence  of  natural  lakes,  artificial  reservoirs  must  be 
made  if  storage  of  water  is  to  be  effected. 

The  question  of  storage  may  either  arise  during  the  period  of 
design,  or  after  a  canal  system  has  been  some  time  in  operation. 
An  artificial  reservoir  may  be  the  essential  feature  of  the 
original  irrigation  project,  and  may  be  required  to  serve  either 
as  the  sole  source  of  supply,  or  as  supplementary  to  a  river  of 
deficient  discharge.  But  the  necessity  of  a  supplementary 


SOURCES  OF  SUPPLY.  49 

reservoir  is  not  always  recognised  during  the  period  of  designing 
an  irrigation  system.  More  often  the  necessity  of  supple- 
menting the  river  discharges  by  storage  does  not  make  itself 
felt  until  the  effect  of  the  irrigation,  carried  on  with  the 
natural  discharge  of  the  river,  has  reached  its  full  development 
and  the  demand  for  water  has  increased  in  consequence  of  an 
unforeseen  expansion  of  the  area  brought  under  cultivation^ 
The  recent  history  of  irrigation  in  Egypt  provides  an 
interesting  example  of  the  latter  conditions.  In  1884  the 
newly  appointed  irrigation  engineers  from  India  commenced 
the  work  of  reform  of  the  irrigation  works  in  Egypt,  which 
they  and  their  successors  have  carried  on  steadily  ever  since. 
As  the  reform  in  means  and  methods  took  effect,  the  cultivation 
became  more  intense  and  the  area  wider,  until  at  length  every 
drop  of  the  summer  discharges  of  the  Nile  was  utilised,  and  no 
further'  development  of  cultivation  was  possible  without  an 
addition  to  the  summer  supply  of  the  river.  During  the  flood 
and  winter  seasons,  however,  there  is  always  enough  water  and 
to  spare  in  the  river,  so  that  there  is  a  surplus  available  in  those 
seasons  for  storage.  The  further  development  of  Egypt  could, 
therefore,  be  promoted  by  the  creation  of  a  reservoir  capable  ol 
holding  this  surplus  water  in  reserve  for  the  summer  months. 
The  study  of  projects  for  its  storage  was,  therefore,  undertaken. 

The  first  calculation  to  be  made,  in  the  particular  case 
selected  as  an  example,  was  one  to  determine  the  quantity 
of  water  v  that  it  was  necessary  to  store  in  order  to  be 
able  to  supplement  the  summer  discharges  of  the  Nile  to  such 
an  extent  that  Egypt  might  receive  its  full  development.  This 
calculation  made,  it  remained  to  decide  to  what  extent  the 
first  reservoir  should  provide  for  this,  and  also  to  ascertain 
whether  there  was  a  sufficiency  of  surplus  discharge  to  furnish 
the  quantity  to  be  stored,  without  inconvenience  to  navigation 
and  other  interests  affected.  To  determine  the  quantity  of 
storage  required,  the  first  thing  to  do  was  to  calculate  the  total 
requirements  of  Egypt.  Experience  has  shown  that  an 

I.  £ 


50  IRRIGATION. 

allowance  of  12  cubic  metres  per  day  per  acre  of  gross  area 
gives  a  sufficient  supply  for  summer  cultivation.1  In  round 
figures  the  area  of  Egypt,  including  areas  to  be  reclaimed  and 
exclusive  of  500,000  acres  to  be  permanently  maintained  as  basin 
land,  may  be  taken  as  7,000,000  acres.  Consequently  the  total 
daily  discharge  required  in  summer  is  84,000,000  cubic  metres. 
The  natural  summer  discharge  of  the  river  may  be  taken  as 
24,000,000  cubic  metres  a  day.  Therefore 60,000,000  cubic  metres 
a  day  is  required  from  the  reservoir  for,  say,  one  hundred  days, 
making  a  total  quantity  to  be  stored  of  6,000,000,000  cubic  metres. 
No  deduction  is  here  made  for  evaporation  in  the  reservoir,  as  the 
summer  discharge  during  the  greater  part  of  the  hundred  days 
is  considerably  greater  than  24,000,000  cubic  metres  a  day,  and 
the  quantity  in  excess  of  that  discharge  may  be  considered  as 
balancing  the  loss  by  evaporation. 

It  was  necessary,  also,  to  decide  the  best  site  for  the  first 
reservoir  to  be  made  and  its  storage  capacity.  At  the  time  that 
these  questions  were  being  considered,  the  Mahdi  was  in  power 
on  the  Upper  Nile,  and  the  examination  of  reservoir  sites  was 
restricted  to  the  river  below  the  second  cataract.  In  con- 
sequence of  this  limitation  of  the  area  of  survey,  Egypt  has 
probably  benefited  by  getting  its  reservoir  some  years  sooner 
than  it  otherwise  would  have  done.  For,  if  the  Upper  Nile 
had  not  been  closed  to  him,  Sir  William  Willcocks,  who  was  in 
charge  of  the  reservoir  study,  would  certainly  have  required  more 
time  for  the  examination  of  other  sites  higher  up  the  river,  and 
he  would,  doubtless,  have  come  to  the  same  conclusion  in  the 
end.  For  there  is  probably  nowhere  on  the  Nile  a  more 
favourable  site  for  the  construction  of  a  dam  than  the  crest  of  the 
first  cataract  above  Assuan,  not  only  on  account  of  the  quality 
of  the  rock  and  the  disposition  of  the  summer  channels,  but 
also  on  account  of  the  site  being  the  nearest  possible  one  that 

1  Recent  calculations  are  based  on  a  larger  allowance.     See  Notes  4  and  5, 
Appendix  IV. 


SOURCES  OF   SUPPLY.  $1 

could  serve  both  Upper  and  Lower  Egypt.  If,  then,  Sir  W. 
Willcocks'  studies  showed  that  the  storage  capacity  of  a 
reservoir  which  could  be  created  by  the  construction  of  a  dam 
at  Assuan  was  sufficiently  ample,  there  was  everything  to 
recommend  the  project,  one  thing  only  excepted,  and  that  the 
resulting  submersion  of  the  island  of  Philae.  The  basin  of  the 
Assuan  reservoir  is  the  valley  itself  through  which  the  Nile  runs. 
Bounded  by  high  rocks,  it  is  of  little  width ;  consequently,  to 
have  capacity,  the  reservoir  had  to  be  deep.  Cross-sections  of 
the  valley  were  taken  to  determine  what  the  capacity  of  the 
valley  was  with  different  water-levels,  in  order  to  furnish  data 
for  a  decision  as  to  the  height  to  which  the  Assuan  dam  should 
be  built.  It  was  calculated  that  a  dam  holding  up  water  to  16 
metres  above  the  natural  low-water  level  would  create  a 
reservoir  capable  of  storing  1,065,000,000  cubic  metres ;  and  that 
if  the  dam  were  made  12  metres  higher,  the  reservoir  capacity 
would  be  increased  to  3,733,000,000  cubic  metres.  Eventually 
it  was  proposed  to  build  a  dam  to  hold  up  to  24  metres  above 
low  water,  and  thereby  to  create  a  reservoir  with  a  storage 
capacity  of  2,550,000,000  cubic  metres.  But  Egypt  was  not  to 
be  allowed  to  go  so  fast.  Strong  protests  from  the  archaeolo- 
gical societies  of  Europe  extracted  a  reluctant  compromise 
from  the  Government  of  Egypt,  and  the  lower  dam  design, 
which  provided  a  storage  of  1,065,000,000  cubic  metres  only, 
was  adopted.  Europe  has  often  interfered  in  the  affairs  of 
Egypt,  not  always  with  advantage  to  the  dwellers  on  the  Nile, 
and,  in  this  case,  with  little  satisfaction  to  itself  At  the  time 
of  making  this  compromise  it  was  calculated  that  the  total 
quantity  of  water  required  to  be  stored  to  supply  the  needs  of 
all  Egypt  and  provide  for  its  full  development  was  3,610,000,000 
cubic  metres,  so  that  the  Assuan  reservoir,  as  decided  on, 
would  hold  less  than  a  third  of  the  total  then  supposed  to  be 
required.  Ten  years  later  the  figure  for  all  Egypt  was  consi- 
dered to  be  6,000,000,000  cubic  metres,1  of  which  the  Assuan 

1  Still  later  the  figure  was  again  increased.     See  Note  5,  Appendix  IV. 

E  2 


52  IRRIGATION. 

reservoir,  as  limited  by  the  compromise,  provided  1,000,000,000, 
leaving  5,000,000,000  still  to  be  arranged  for. 

As  the  sources  of  supply  for  an  irrigation  scheme  are  being 
considered,  and  Egypt  furnishes  a  concrete  example  of  a  country 
seeking  means  to  still  further  increase  its  water  supply,  it  may  be 
interesting  to  examine  the  suggestions  which  were  made  at  that 
time  to  obtain  the  increase.  There  were  five  possible  ways  of 
doing  it  as  then  conceived  : — 

(1)  The  Assuan  dam  might  be  raised,  and  the  capacity  of  its 
reservoir  doubled.     (The  raising  of  the  Assuan  dam  was  decided 
upon  in  1906  and  the  work  was  completed  in  1912.     Ths  wxtra 
storage  thus  obtained  is  1,200,000,000  cubic  metres.) 

(2)  Another  dam,  similar  to  the  Assuan  dam,  might  be  built 
on  the  river  at  some  suitable  point  higher  up,  to  form  another 
reservoir  in  the  Nile  valley  itself  j1 

(3)  A  reservoir  might  be  created  in  a  depression  known  as 
the  Wadi  Rayan,  alongside  the  Fayum  province,  which  would 
be  close  to  the  site  of  Lake  Mceris,  and  would  act  in  much  the 
same  way  as  the  ancient  reservoir,  though  it  would  be  on  a 
smaller  scale ; 

(4)  The  loss  by  evaporation  and  absorption,  where  the  river 
spreads    itself    out     through    the    Sudd    region,    might    be 
enormously  reduced ; 

(5)  The  lakes  near  the  equator  at  the  White  Nile   sources 
might  be  controlled  by  regulation  so  as  to  serve  as  storage 
reservoirs. 

Enough  has  already  been  said  about  the  Assuan  reservoir 
and  Lake  Moeris  to  show  in  what  way  the  first  three  alternative 
projects  would  provide  for  feeding  the  river  at  low  supply,  and 
on  what  data  the  calculations  concerning  their  utility  would 
be  based.  The  fourth  method  of  increasing  the  supply,  by 
diminishing  the  loss  due  to  evaporation  and  absorption,  is  an 
unusual  one,  and  the  proposal  is  the  outcome  of  the  peculiar 
conditions  of  the  Upper  Nile  above  Khartoum. 

1  A  project  for  a  barrage  on  the  White  Nile  is  approved ;  but  it  is  not 
similar  to  the  Assuan  dam.  See  Note  6,  Appendix  IV. 


SOURCES  OF   SUPPLY. 


53 


On  the  long  line  of  river  lying  between  the  equatorial  lakes 
and  Khartoum  (see  Fig.  6)  the  swamps,  known  as  the  Sudd 
region,  are  traversed  by  the  flowing  water  for  a  distance  of 
nearly  500  miles.  In  these  swamps  the  river  spreads  itself 


THE    NILE! 
ABOVE 

KHARTOUM 


Fl  G 


KHARTOUM        «• 


LAKE 
ALBERT 
EDWARD 


OH      f K L L 8 


out  over  a  vast  area  of  unknown  extent,  escaping  sideways  from 
the  two  more  or  less  well-defined  channels  into  which  the  river 
divides  itself  where  it  enters  the  marsh  tract.  Over  this  expanse 
of  water-surface  evaporation  is  active,  while  the  papyrus  and 
other  swamp-loving  plants,  stretching  away  in  all  directions 
without  visible  limits,  have  a  power  of  absorption  proportional 


54  IRRIGATION. 

to  the  vast  extent  that  they  cover.  Discharge  observations  have 
shown  that,  of  the  water  which  enters  at  the  upper  end  of  the 
swamps,  50  per  cent,  is  lost  in  summer  and  75  per  cent,  in  a 
high  flood.  The  actual  measurements  give  the  following 
results.  During  summer  the  discharge  entering  the  swamps 
at  Lado  is  600  to  700  cubic  metres  a  second,  of  which  only 
300  finds  its  way  out  at  the  lower  end  of  the  Sudd  region.  In  a 
low  flood  the  discharge  entering  is  1,000  cubic  metres  a  second, 
of  which  400  reappears  ;  in  a  high  flood  2,000  enters,  and  500 
comes  out  again. 

If,  then,  this  loss  could  be  entirely  prevented,  the  summer 
discharge  of  the  river  could  be  increased  from  300  cubic  metres 
a  second  to  600  at  the  point  where  it  leaves  the  swamps.  This 
would  represent  an  increase  of  26,000,000  cubic  metres  a  day 
(over  10,000  cubic  feet  a  second),  which  would  go  a  long  way 
towards  making  good  the  present  deficiency  of  the  water  supply 
of  Egypt ;  for  the  increase  would  be  equivalent  to  that  which 
would  be  obtained  from  a  reservoir  storage  of  2,500,000,000 
cubic  metres.  One  great  advantage  in  this  method,  over  that 
of  storage  in  reservoirs,  is  that  the  river  supply  is  not  decreased 
at  any  time  of  the  year  in  order  to  obtain  an  increase  at  another, 
but  is  increased  at  all  seasons,  a  matter  of  some  importance 
when  the  quantity  still  required  to  supplement  the  river  in 
summer  reaches  such  a  high  figure  as  5,000,000,000  cubic 
metres  according  to  the  then  accepted  estimate. 

The  method  proposed,  with  the  object  of  diminishing  the 
enormous  loss  of  water  in  the  Sudd  region,  is  to  form  an 
embanked  channel  from  end  to  end  of  the  swamps  in  order  that 
the  river  discharge  may  be  prevented  from  spilling  sideways 
except  at  such  times  and  places  as  may  be  found  desirable.  It 
would  not  be  economical  or  even  advantageous  to  form  a 
channel  large  enough  to  carry  the  flood  discharge ;  therefore 
some  provision  would  have  to  be  made  for  disposing  of  the 
surplus  water.  The  original  suggestion  was  to  construct 
regulating  works  at  the  head  of  the  proposed  channel,  so  that 


SOURCES   OF   SUPPLY.  55 

only  the  required  discharge  should  be  allowed  to  flow  into  it, 
and  the  surplus  be  escaped  through  masonry  sluices  to  spread 
about  at  will  in  the  swamps  and  be  evaporated  and  absorbed.^ 
But  a  later,  and  probably  better,  proposal  has  been  made  for 
the  disposal  of  this  surplus,  and  that  is,  to  prevent  it  from 
leaving  the  upper  lakes  at  the  river  sources,  and  so  to  keep  it 
in  reserve  till  it  is  wanted.  The  area  of  the  lower  and  smaller 
lake,  the  Albert  Nyanza,  is  so  great  that  a  regulating  work  at 
its  outlet,  designed  to  hold  up  not  more  than  3  metres  (10  feet), 
would  probably  give  all  the  control  necessary.  The  regulation 
of  the  outflow  of  Lake  Albert  is  another  matter  connected  with 
the  storage  question.  At  present  the  subject  under  considera- 
tion is  the  method  of  adding  to  the  available  supply  in  the  lower 
reaches  of  the  river  by  the  avoidance  of  loss  in  the  upper  reaches. 
In  the  example  selected  for  illustration  the  means  of  prevention 
consists  in  arrangements  to  lessen  the  waste  by  the  confinement 
of  the  discharge  in  a  channel  of  uniform  section  adapted 
to  its  volume.  In  the  particular  instance  of  the  Nile  swamps 
the  difficulty  lies  in  selecting  the  most  favourable  alignment  for 
the  channel,  and  in  executing  the  work  when  the  line  has  been 
chosen.  Either  an  existing  channel  must  be  enlarged  and 
embanked,  or  a  new  canal  and  banks  be  made  along  whatever 
alignment  may  be  found  to  be  the  most  favourable.  The 
shortest  distance  possible  would  be  that  of  a  straight  line 
joining  the  river  at  Bor  with  the  point  where  the  Sobat  river 
ends  in  the  White  Nile,  the  length  of  which  is  210  miles,  as 
shown  in  Fig.  6.  The  distance  between  the  same  points, 
following  the  windings  of  the  existing  principal  channel,  is 
440  miles,  or  more  than  double  the  distance  along  the  straight 
line.  The  length  of  channel  to  be  formed  must,  therefore,  be 
something  between  440  and  210  miles.  This  would  in  any 
case  be  a  formidable  undertaking,  but  it  is  one  which,  if  it 
proved  successful,  would  fully  justify  a  very  high  expenditure. 
But  though  the  loss  of  water  may  be  materially  decreased,  it 
cannot  be  entirely  prevented,  as  there  must  be  some  consider- 


56  IRRIGATION. 

able  loss  from  evaporation  and  absorption  in  a  canal  of  300  miles 
length,  more  or  less,  lying  wholly  within  the  tropics.  Even  if 
there  were  none,  and  the  discharge  at  the  head  reached  the  tail 
in  undiminished  volume,  the  full  requirements  of  Egypt  would 
still  not  be  met,  and  additional  storage  somewhere  would 
be  necessary. 

If  one  or  more  of  the  three  alternative  projects  of  storage 
already  enumerated  is  not  selected  to  supply  the  deficiency, 
there  still  remains  the  fifth  alternative  of  controlling  the  water 
that  leaves  the  equatorial  lakes.  That  the  lowest  lake  of  the 
thres,  the  Albert  Nyanza,  has  capacity  enough  to  store  all 
that  is  wanted  with  a  heading  up  of  a  few  feet  only,  is  easily 
shown.  The  surface  area  of  the  lake  is  4,500  square  kilo- 
metres. Before  the  Assuan  dam  was  made  Egypt  was  in  need 
of  6,000,000,000  cubic  metres  of  stored  water  for  use  in  summer. 
The  Assuan  reservoir,  now  that  the  raising  of  the  dam  is  com- 
plete, supplies  2,300,000,000.  The  formation  of  an  embanked 
channel  through  the  swamp  region  would  effect  an  increase  of 
the  summer  discharge  equivalent  to  that  produced  by  a  storage 
of,  say,  1,700,000,000  cubic  metres.  Consequently  a  further 
storage  of  2,000,000,000  cubic  metres  was  required,  according  to 
the  accepted  figures  of  those  days.  It  is  difficult  to  estimate 
what  proportion  of  such  an  increase  would  be  lost  on  the  long 
journey  (some  3,000  miles)  from  the  lakes  to  Egypt,  but  it  would 
not  be  very  great,  as  a  moderate  addition  to  an  existing  supply 
would  only  slightly  increase  the  evaporating  and  absorbing 
areas.  Hence,  if  3,000,000,000  cubic  metres  of  storage  is 
effected,  it  may  be  considered  that  sufficient  allowance  has  been 
made  for  loss  on  the  way,  the  allowance  being  33  per  cent. 
The  area  of  Lake  Albert  being  4,500  square  kilometres,  or 
4,500,000,000  square  metres,  a  layer  of  70  centimetres  (or 
2  J  feet)  depth  would  represent  a  stored  volume  of  3,150,000,000 
cubic  metres  ;  and  that  is  about  what  is  wanted  according  to 
the  data  assumed  as  to  the  total  requirements. 

It  has  now  to  be  ascertained  if  the  quantity  of  rain  that 


SOURCES   OF   SUPPLY.  57 

reaches  the  lake  from  the   gathering   gronnd  is  sufficient  to 
provide  for  that  storage.     There  are,  in  this  particular  case, 
two  ways  of  calculating  what  the  quantity  available  for  use  is. 
The  one  method  is  to  calculate  the  quantity  from  what  flows 
into  the  lake  from  the  gathering  ground ;  and  the  other,  and 
more  accurate  method,  is  to  make  the  calculation  from  what 
leaves  the  lake.     As  reliable  data  for  making  the  calculation 
by  the  former  method  do  not  exist,  the  second  method  alone 
can  be  usefully  applied  to  this  case.     The  mean  discharge  of 
the  Alb<  rt  Nyanza  outflow  for  the  year,  measured  in  the  river 
below  the  outlet  of  the  lake,  is  officially  given  as  769  cubic 
metres  a  second.     Assuming  that  the  numerous  torrents  which 
feed  the  river  between  the  lake  outlet  and  the  head  of  the 
proposed  new  channel  give  a  sufficient  discharge  without  any 
help  from  the  lakes  for  the  four  months  of  high  supply,  the 
volume  of  the  discharge  of  the  Albert  Lake  outlet  could  be 
entirely  stored  in  the  lake  for  these  four  months,  and  be  added 
to  the  normal  discharge  during  the  remaining  eight  months. 
The  quantity  stored  would  be  at  the  rate  of  769  cubic  metres  a 
second  for  four  months,  and  the  addition  to  the  normal  dis- 
charge for  the  remaining  eight  months  would,  therefore,  be 
half  that  figure,  or  384  cubic  metres  a  second,  equivalent  to 
33,000,000  cubic  metres  a  day,  or  a  storage  of  3,300,000,000 
cubic   metres   for   use   during  the  low   supply  period  of  one 
hundred  days.     So    it  may   be    concluded  that,    if  the   data 
are   correct,  the  storage  possibilities  of   the  equatorial  lakes 
are  not  much  more  than  sufficient  to  satisfy  Egypt,  even  after 
the  Sudd  channel  has  minimised  the  loss  in  transit  through  the 
swamps.1 

With  the  help  of  illustrations  borrowed  from  the  Nile,  the 
following  instances  of  water  supply  have  been  passed  in  review : 
firstly,  a  supply  derived  from  the  natural  discharge  of  a  river 
unaided  by  any  reservoir ;  then,  of  a  river  with  a  lateral  reservoir 
to  supplement  its  lower  branches;  again,  of  a  river  supple- 

1  See  Note  4,  Appendix  IV. 


58  IRRIGATION. 

mented  by  a  reservoir  made  in  the  valley  of  the  river  itself  far 
below  its  sources ;  then  again,  of  a  river  discharge  being 
increased  by  prevention  of  waste  on  the  line  of  flow ;  and 
lastly,  of  a  river  fed  by  natural  reservoirs  brought  under 
control  by  engineering  works  of  regulation.  "  There  remains 
one  more  class  of  reservoirs,  of  which  the  Nile  furnishes  no 
example,  but  which  is  perhaps  the  most  common  in  other 
countries.  This  class  includes  artificial  reservoirs  made  in 
the  upper  part  of  the  catchment  of  a  river.  Such  a  reservoir  is 
formed  by  the  construction  of  a  dam  on  the  most  convenient 
site — usually  across  a  gorge — whereby  the  discharges  of  the 
higher  tributary  streams  are  intercepted  and  retained  in  the 
valley  which  is  converted  into  a  reservoir  by  the  dam. 

The  Indian  Irrigation  Commission  (1901 — 1903)  in  its  report, 
among  other  recommendations  for  storage  works  in  many  parts 
of  India,  proposes,  in  the  interests  of  the  Deccan  districts  of 
Bombay,  "  that  the  catchment  areas  of  all  the  rivers  which 
derive  their  supplies  from  the  unfailing  rainfall  of  the  Western 
Ghats  should  be  carefully  examined  with  a  view  to  the  con- 
struction of  as  many  large  storage  reservoirs  as  possible,  and  of 
the  works  necessary  for  carrying  the  supply  into  those  tracts  in 
which  irrigation  is  most  urgently  needed." 

Sir  Thomas  Higham,  who  was  one  of  the  members  of  the 
Indian  Irrigation  Commission,  stated  in  the  discussion  on  Irri- 
gation, St.  Louis  Exhibition  Congress,  1904,  that  "  almost  all 
future  extensions  of  irrigation  in  India,  with  the  exception  of 
the  large  canals  that  are  still  possible  in  Northern  India  and  in 
Sind,  will  involve  the  construction  of  storage  works." 

In  the  United  States  further  progress  in  the  irrigation  of  the 
arid  regions  can  only  be  brought  about  by  the  storage  of  flood 
waters  in  reservoirs.  For  nearly  the  whole  available  flow  of 
the  streams  has  already  been  appropriated  by  means  of  such 
irrigation  works  as  are  within  the  power  of  individuals,  corpora- 
tions or  societies  to  carry  out.  But  the  more  formidable 
engineering  works  that  are  necessary  to  effect  storage  are  out- 


SOURCES  OF  SUPPLY.  59 

side  the  possible  limits  of  private  enterprise,  and  fall  within  the 
province  of  Government  to  execute.  President  Roosevelt  in 
his  first  message  to  Congress,  1901,  admits  this  in  the  following 
words :  "  Great  storage  works  are  necessary  to  equalise  the 
flow  of  streams  and  to  save  the  flood  waters.  Their  construc- 
tion has  been  conclusively  shown  to  be  an  undertaking  too 
vast  for  private  effort.  ...  It  is  as  right  for  the  national 
Government  to  make  the  streams  and  rivers  of  the  arid  region 
useful  by  engineering  works  for  water  storage  as  to  make  use* 
ful  the  rivers  and  harbours  of  the  humid  region  by  engineering 
works  of  another  kind." 

The  agricultural  development  of  South  Africa  depends  also 
to  a  great  extent  upon  the  storage  of  water  in  reservoirs. 

The  essential  feature  of  such  storage  works  as  those  contem- 
plated in  India  and  the  United  States  will  be,  in  some  cases, 
a  high  dam  designed  after  the  type  of  dams  already  built  for 
similar  purposes,  of  which  examples  will  be  given  in  the  next 
chapter. 

Obviously  the  first  condition  that  should  be  satisfied  by  any 
storage  project  is  that  there  shall  be  a  sufficient  volume  of  flow- 
off  the  catchment  above  the  dam  to  fill  the  reservoir  to  the  height 
necessary  to  provide  adequate  storage  for  the  year's  requirements 
in  any  year  of  which  the  rainfall  is  not  exceptionally  bad.  The 
site  of  the  reservoir  must  therefore  be  at  a  suitable  distance  below 
the  actual  sources  of  the  river  system  to  which  it  belongs.  If  the 
dam  is  to  be  a  high  one,  it  must  have  sound  rock  for  its  founda- 
tion. Gorges,  at  the  outlet  of  a  mountain  valley,  from  which 
the  hill-slopes  above  recede  widely  so  as  to  enclose  an  expansive 
area,  are  the  most  favourable  sites  for  dams.  The  height  of 
the  dam  will  be  determined  by  the  quantity  that  the  reservoir 
is  to  be  made  to  hold  and  by  the  configuration  of  the  basin 
formed  above  it.  A  basin  or  valley  with  a  gradually  sloping 
bed  will  require  a  less  height  of  dam  to  effect  the  storage  of 
a  given  quantity  than  will  be  necessary  if  the  slope  of  the  bed 
is  more  rapid.  But  a  deep  reservoir  has  this  advantage  over  a 


6O  IRRIGATION. 

shallow  one,  that  a  less  proportion  of  water  is  lost  by  evapora- 
tion. 

It  was  remarked  above  that  the  scientific  boundaries  of 
tracts  of  country,  hydrographically  considered,  are  the  water- 
sheds between  their  catchments.  This  scientific  division  has 
been,  in  some  cases,  upset  by  irrigation  engineers  themselves 
refusing  to  be  bound  by  it.  There  are  instances  of  the  water 
supply  of  one  catchment  being  diverted  into  a  neighbouring 
catchment  by  carrying  it  round  or  through  the  water-shed 
ridge.  This  has  been  done  on  the  Rocky  Mountains  in 
Colorado.  On  the  west  side  the  supply  exceeds  the  demand, 
but  on  the  east  there  is  less  than  enough.  Consequently  the 
supply  of  the  west  has  been  carried  in  channels  or  tunnels  to 
the  east  side  of  the  water-shed,  and  made  to  do  duty  there. 
"The  Sky  Line  ditch,"  to  cite  a  particular  instance,  carries 
water  in  a  channel  cut  in  the  rock  round  the  mountain  tops  at 
an  altitude  of  10,000  feet,  and  diverts  it  from  one  of  the  upper 
tributaries  of  the  Laramie  river  to  Cache-la-Poudre  valley, 
Colorado. 

There  is  a  remarkable  instance  of  the  diversion  of  the  water 
of  one  catchment  into  another  to  be  found  in  India.  The 
district  of  Madura,  in  Southern  India,  has  frequently  suffered 
from  famine,  lying  as  it  does  on  the  eastern  side  of  the  Ghats, 
where  the  rainfall  is  scanty  and  very  uncertain.  On  the 
western  side  of  the  Ghats,  however,  the  rainfall,  which  is 
copious  and  unfailing,  under  natural  conditions  finds  its  way 
down  the  channel  of  the  Periyar  river  and  discharges  itself 
uselessly  into  the  sea.  At  one  point  in  its  course  the  Periyar  river 
is  separated  by  a  few  miles  only  from  one  of  the  tributaries  of 
the  Vaigai,  the  river  of  the  eastern  catchment  on  which  Madura 
relies  for  its  irrigation.  At  this  point  a  channel  of  connection  has 
been  made  between  the  Periyar  and  Vaigai  rivers,  and,  in  addition, 
a  reservoir  has  been  formed  on  the  Periyar  river  for  storing  the 
rainfall  of  its  catchment.  The  Vaigai  is  thus  fed  by  the  rain  which 
falls  on  the  other  side  of  the  water-shed  separating  it  from  the 


SOURCES  OF  SUPPLY.  6 1 

Periyar  catchment.  The  connection  between  the  two  consists  of 
a  tunnel  cut  in  the  rock  through  the  intervening  hills,  5,704  feet 
in  length.1  The  reservoir  of  the  Periyar  river  is  formed  by  a 
dam,  1,241  feet  in  length  and  155  feet  in  height  from  river 
bed  to  crest,  built  across  a  very  narrow  gorge.  The  reservoir 
holds  13,300,000,000  cubic  feet  of  water,  of  which  the  upper 
6,815,000,000  only  are  available  for  irrigation.  The  catchment 
above  the  dam  has  an  area  of  about  300  square  miles,  and  the 
rainfall  is  said  to  be  more  than  120  inches  in  the  year.  The 
reservoir  has  a  water-spread  of  about  12  square  miles.  But  it 
is  not  only  the  amount  stored  that  is  available  for  irrigation  on 
the  Vaigai,  but  the  discharge  of  the  Periyar  river  as  well ;  so 
that  altogether  a  total  volume  of  about  30,000,000,000  cubic 
feet  is  diverted  during  the  year  from  one  catchment  to  the 
other. 

A  bold  project  has  been  recently  undertaken  in  India,  which 
also  depends  for  its  working  on  the  use  of  the  water  of  one 
catchment  for  irrigation  in  another.  A  reservoir  does  not  form 
a  feature  in  this  project,  as  the  rivers  concerned  are  snow-fed. 
The  rivers  are  the  Jhelum  on  the  west,  the  Chenab  in  the 
middle,  and  the  Ravi  on  the  east.  There  is  land  requiring 
irrigation  between  the  Jhelum  and  the  Chenab,  also  between 
the  Chenab  and  the  Ravi,  and  again  on  the  east  of  the  Ravi. 
The  Chenab  and  the  Ravi  have  no  water  to  spare,  as  existing 
irrigation  has  claims  to  the  whole  supply.  But  there  is  water 
to  spare  in  the  Jhelum.  So  it  was  decided  to  carry  the  surplus 
of  the  Jhelum  across  to  the  Chenab,  and  thus  release  a  corre- 
sponding volume  of  the  Chenab  discharge  for  the  irrigation  of 
the  tracts  to  the  east  of  it.  This  discharge  is  carried  in  a  canal 
which  irrigates  the  land  alongside  it  between  the  Chenab  and 
Ravi  rivers,  and  then  passes  the  Ravi  river  by  a  level  crossing 
to  irrigate  the  lands  to  the  east  of  the  Ravi.1 

Further  particulars  concerning  some  of  the  more  important 
reservoirs  and  dams  already  constructed  or  projected  will  be 

1  See  Note  7,  Appendix  IV. 


62  IRRIGATION. 

given  in  the  next  chapter.  But  before  leaving  the  subject  of 
supply,  mention  must  be  made  of  one  of  the  earliest  systems  of 
irrigation  in  India — the  system  of  surface  tanks.  Thousands 
of  these  tanks  in  Madras  provide  irrigation  for  millions  of  acres 
of  rice  crops.  They  vary  in  size  from  a  few  acres  to  nine  or  ten 
square  miles  of  water  surface.  They  are  usually  formed  by 
earthen  embankments  thrown  across  small  local  drainages, 
often  of  only  two  or  three  square  miles  in  area,  or  by  a  series 
of  such  embankments  thrown  across  the  valleys  leading  from 
larger  catchments  The  Madras  tanks  depend  mainly  on  local 
rainfall,  but  are  sometimes  fed  from  rivers  or  streams  by  means 
of  channels  taking  off  above  weirs  constructed  in  the  beds  of 
the  rivers. 

The  relative  importance  of  the  tank  system  in  India,  as 
compared  with  other  systems  of  supply,  may  be  gathered  from 
the  following  figures  : — 

Area  in  British  India  irrigated  from  wells         .  13,000,000  acres. 

„  „  „  „     canals        .  17,000,000     j,    ", 

„  „  „  „    tanks         .  8,000,000      „ 

„  „  ,,         in  various  ways      6,000,000      „ 

Total  area  in  British  India  irrigated  .    44,000,000      „ 

Tanks  are  the  primitive  forms  from  which  the  more  modern 
and  imposing  reservoir  has  been  evolved ;  but  as  the  early 
form  is  so  well  adapted  to  certain  conditions,  it  has  survived, 
with  but  little  modification,  in  those  situations  where  the 
conditions  favourable  to  development  to  the  higher  type  do 
not  exist. 

In  the  United  States  there  is  a  class  of  reservoirs  which  in 
some  respects  resemble  the  Indian  tanks.  They  are  formed  in 
suitable  places  among  the  foothills  or  out  on  the  plains  where 
convenient  depressions  exist  in  the  neighbourhood  of  irrigable 
farms.  They  are  filled  by  large  canals,  taking  off  from  a  river, 
with  the  surplus  discharge  which  may  not  be  needed  for  direct 
irrigation,  either  during  the  flood  or  other  seasons.  From  these 
river-fed  reservoirs  the  water  is  carried  in  canals  to  the  fields  to 
be  irrigated. 


CHAPTER   V. 

DAMS  AND    RESERVOIRS. 

THE  further  agricultural  development  of  India,  Egypt,  the 
Western  States  of  America,  Western  Canada,  South  Africa, 
Spain  and  other  arid  countries  depends  largely  on  irrigation. 
In  the  countries  named,  Canada  only  excepted,  almost  all  future 
extensions  of  irrigation  will  involve  the  construction  of  storage 
works.  The  subject  of  reservoirs  has,  therefore,  an  increasing 
importance  to  the  present-day  student  of  irrigation. 

The  climatic  conditions  which  create  a  demand  for  and  favour 
the  formation  of  storage  reservoirs  are  a  deficient  or  uncertain 
rainfall  during  the  period  of  the  growth  of  crops,  and  at  other 
seasons  a  constant  and  heavy  rainfall  over  the  area  from  which 
the  crops  obtain  their  water  supply.  Such  are  the  conditions 
which  are  usually  associated  with  perennial  irrigation,  and  it  is 
this  which  explains  the  almost  universal  need  of  storage  works 
in  countries  which  have  dry  and  rainy  seasons.  The  more 
valuable  crops,  as,  for  instance,  sugar-cane  and  cotton,  are 
those  which  require  watering  during  the  spring  or  summer 
months,  when  the  natural  water  supply  is  often  at  its  lowest. 

Before  looking  for  a  reservoir  site,  it  is  necessary  to  ascertain, 
from  such  rainfall  statistics  as  may  exist,  whether  a  reservoir,  if 
made,  will  fill  with  sufficient  regularity  to  justify  confidence 
being  placed  in  it  as  k  reliable  insurance  against  deficiency  of 
supply.  *  If  the  rainfall  statistics  give  encouragement  enough, 
the  catchment  area  should  be  examined  with  a  view  to  selecting 
a  favourable  site  for  a  reservoir.  The  nearer  the  reservoir  is  to 
the  land  to  be  irrigated  the  better,  for  several  reasons.  Not 
only  will  the  loss  of  water  in  transit  between  reservoir  and  crop 


64  IRRIGATION. 

from  evaporation  and  absorption  be  less,  and  the  accommoda- 
tion of  the  supply  to  the  demand  be  easier,  but  the  extent  of  the 
collecting  area  will  be  greater  than  it  would  be  if  the  reservoir 
were  removed  to  a  site  higher  up  the  catchment  basin.  But, 
as  a  rule,  the  configuration  of  the  ground  determines  the  best 
site  for  the  reservoir,  and  the  selection  of  the  site  is  not  so  much 
a  matter  of  choice  as  a  recognition  of  Nature's  decision  in  the 
matter. 

When  the  situation  of  the  future  reservoir  is  known,  the 
question  of  its  annual  replenishment  can  be  studied.  The 
period  and  amount  of  rainfall,  the  proportion  of  flow-off  to 
total  rainfall,  and  the  area  of  the  catchment,  are  the  necessary 
data  required  for  the  determination  of  the  question.  The 
catchment  area  can  generally  be  measured  with  sufficient 
accuracy  on  existing  maps;  otherwise  a  survey  will  have  to 
be  undertaken  to  ascertain  the  lie  of  the  watershed  lines  and 
the  area  enclosed  by  them.  The  rainfall  statistics  are  generally 
imperfect,  and  the  proportion  of  flow-off  a  most  difficult  thing 
to  estimate.  <  That  the  rainfall  statistics  are  usually  imperfect 
is  not  surprising,  considering  what  is  held  to  constitute  com- 
pleteness of  the  rainfall  record.  It  is  not  enough  to  have  the 
rainfall  readings  of  one  or  two  stations  in  the  catchment. 
The  observations  must  be  made  in  at  least  as  many  sites  in  the 
catchment  as  will  give  values  representative  of  all  the  local 
variations  in  the  annual  amount  of  the  rainfall.  Moreover,  to 
include  all  the  cyclical  changes,  the  statistics  should  embrace 
the  observations  of  thirty-five  years,  as  less  than  this  may  not 
include  years  of  extreme  conditions.  If,  however,  the  records 
do  not  exist,  there  is  no  choice  but  to  make  the  best  of  imperfect 
data,  and  to  allow  a  wide  margin  of  safety. 

But,  even  though  the  rainfall  statistics  may  be  as  complete 
as  could  be  desired  and  the  catchment  area  accurately  known, 
there  will  still  remain  much  uncertainty  as  to  the  quantity  that 
will  reach  the  impounding  basin.  Only  a  proportion  of  the 
rain  that  falls  on  the  catchment  area  flows  off  it.  The  rest 


DAMS   AND   RESERVOIRS.  65 

is  evaporated  or  absorbed.  The  amount  that  is  evaporated 
varies  with  the  temperature  and  the  hygrometric  condition  of 
the  air.  The  amount  absorbed  varies  with  the  nature  of  the 
soil  and  its  degree  of  dryness  or  saturation  at  the  time  of  rain- 
fall, and  depends  on  the  surface  slope  and  configuration  of  the 
collecting  basin,  and  on  the  presence  or  absence  of  trees  or 
smaller  vegetable  growth.  The  proportion  of  flow-off  is  also 
affected  by  the  intensity  of  the  rainfall.  In  Chapter  IV.  of 
Buckley's  "  The  Irrigation  Works  of  India,"  and  in  Strange's 
"Indian  Storage  Reservoirs,"  valuable  statistics  of  ''flow-off" 
from  different  catchments  in  India  are  collected,  and  the  con- 
clusions to  be  drawn  from  them  discussed.  It  appears  that 
the  conditions  of  rainfall  and  catchment  may  vary  to  such  an 
extent  that  the  proportion  of  flow-off  to  total  rainfall  may 
correspondingly  vary  from  nothing  to  98  per  cent.  It  would 
seem,  then,  almost  a  waste  of  labour  to  attempt  to  calculate 
the  quantity  of  water  that  will  reach  the  reservoir  with  factors 
of  which  one  is  so  variable  as  the  figure  representing  the  pro- 
portion of  flow-off.  And  so  perhaps  it  would  be  in  the  absence 
of  a  somewhat  intimate  knowledge  of  the  nature  of  the  catch- 
ment area  and  of  its  rainfall,  or  without  the  experience  necessary 
to  make  correct  deductions  from  such  knowledge.  Consequently 
it  is  better,  whenever  it  is  possible,  to  base  the  estimate  of  the 
quantity  of  flow-off  on  the  discharges  of  the  streams  which 
actually  drain  the  area,  if,  by  any  means,  they  can  be  even 
approximately  determined. 

Still,  the  subject  of  calculating  quantities  of  flow-off  by 
means  of  rainfall  and  catchment  figures  cannot  be  dismissed 
by  throwing  discredit  on  the  data  commonly  available,  as  there 
may  be  no  other  method  possible  of  arriving  at  any  conclusion 
concerning  the  prospects  of  filling  the  reservoir  and  as  to  the 
allowance  of  escape  waterway  that  must  be  provided  to  pass 
off  any  excess  reaching  the  reservoir  when  it  is  full.  The  flow- 
off  and  its  relation  to  the  rainfall  have  been  carefully  studied 
in  the  case  of  many  reservoirs  in  India,  and,  in  the  hands  of 

i.  r 


66 


IRRIGATION. 


anyone  competent  to  make  proper  use  of  it,  the  record  of  the 
observations  made  forms  a  useful  guide  for  estimating  the 
flow-off  from  catchments  which  are  known  to  have  similar 
characteristics  to  any  of  those  to  which  the  record  applies. 

Perhaps  the  conditions  which  most  affect  the  proportion  of 
the  flow-off  are  the  state  of  the  catchment  at  the  time  of  rainfall 
and  the  intensity  of  the  rainfall.  Mr.  Strange  gives  the  follow- 
ing figures  as  a  rough  approximation  of  what  may  be  expected 
from  an  ordinary  drainage  area : — 


Condition  of  the  Catchment. 

Inches  in 
Twenty-four 

Percentage  of  Flow-off  to  Rainfall. 

Hours. 

Dry. 

Damp. 

Wet. 

0-25 

Nil. 

Nil. 

12 

0'50 

Nil. 

10 

14 

I  -00 

5 

14 

20 

2'OO 

IO 

25 

34 

3'00 

20 

40 

55 

4'00 

30  to  40 

50  to  60 

70  to  80 

and  over. 

In  India  it  has  been  found  that,  in  tracts  where  the  rainfall 
in  the  five  monsoon  months  is  about  40  inches,  the  percentage 
of  flow-off  has  an  average  monthly  variation  represented 
approximately  by  the  following  figures : — 

Assumed  Rainfall.  Flow  off. 

June      .  .        6  inches  —    5  per  cent,  of  rainfall. 

July       •  .  ii       „      — 15 

August.  .  ii       „      —  35  „  „ 

September  .        8       „       —  50  „  „ 

October  4      „      —  30  „ 


With  a  monsoon  rainfall  of  less  than  40  inches  the  percentage 
of  flow-off  would  be  less.  These  figures,  however,  must  only 
be  taken  as  relatively  correct,  and  as  indicating  in  a  rough  way 
the  manner  in  which  the  percentage  of  flow-off  varies  with  the 
saturation  of  the  soil  and  the  intensity  of  the  rainfall. 


DAMS   AND   RESERVOIRS.  6? 

The  result  of  the  calculations  of  flow-off  will  serve  to  show 
(if  the  data  used  have  been  correct)  whether  the  catchment 
will  furnish  the  quantity  of  water  required  to  make  the  reservoir 
a  success  as  a  main  or  supplementary  source  of  supply  to  an 
irrigation  system.,  To  be  a  success,  the  supply  must  not  fail 
in  years  of  deficient  rainfall ;  though  some  hold  that  it  is  not 
necessary  to  insist  that  it  must  be  equal  to  the  demand  in  years 
of  exceptionally  scanty  rainfall,  which  come  but  seldom. 
Whether  shortcomings  in  such  years  may  be  deliberately  con- 
templated as  admissible  in  the  preparation  of  a  reservoir 
project,  must  depend  on  the  circumstances  of  the  particular 
case.  But  a  reservoir  which  fills  in  years  of  ordinary  rainfall 
when  its  assistance  may  not  be  much  wanted,  and  fails  to  fill 
in  years  of  deficient  rainfall  when  there  is  urgent  need  of  its 
help,  does  not  justify  its  existence  and  the  cost  of  its 
construction. 

Assuming,  however,  that  the  study  of  the  rainfall  and  catch- 
ment conditions  have  led  to  the  conclusion  that  the  replenish- 
ment of  the  reservoir  is  assured,  there  remains  another  matter 
to  investigate.  It  is  most  important  to  determine  the  maximum 
discharge  that  the  by-wash  or  escape  of  the  reservoir  will  have 
to  pass.  An  under-estimate  of  what  this  may  be  might  be 
followed  by  disastrous  results.  The  fate  of  the  Nadrai 
aqueduct  in  India  conveys  an  impressive  lesson.  This 
aqueduct  carried  the  Lower  Ganges  Canal  over  the  Kali  Nadi, 
a  channel  which  drains  an  area  of  2,377  square  miles.  The 
waterway  allowed  under  the  aqueduct  for  the  discharge  of  the 
Kali  Nadi  was  calculated  on  the  basis  of  the  then  highest 
recorded  flood  of  23,000  cubic  feet  a  second,  equivalent  to 
9  cubic  feet  a  second  per  square  mile  of  drained  area,  or 
0*33  inches  in  depth  over  the  entire  catchment  in  twenty-four 
hours.  In  July,  1885,  a  flood  of  130,000  cubic  feet  a  second — 
six  times  as  great  as  the  maximum  previously  recorded — caused 
a  rise  at  the  aqueduct  of  20  feet  above  the  highest  water  mark 
of  previous  years,  and  destroyed  the  work.  The  aqueduct  has 

F  2 


68  IRRIGATION. 

since  been  rebuilt  and  a  sufficient  waterway  provided  for  the 
safe  passage  of  140,000  cubic  feet  a  second,  which  is,  since  the 
accident,  the  accepted  figure  for  the  maximum  discharge  of  the 
Kali  Nadi. 

To  guard  against  such  an  unwelcome  surprise  as  was 
experienced  in  the  case  of  the  Nadrai  aqueduct,  it  is  necessary 
to  ascertain  the  maximum  discharge  from  the  catchment  in 
periods  of  heaviest  rainfall  and  greatest  flow-off.  So  it  is 
desirable  to  have  a  record,  not  only  of  the  daily  rainfall,  but 
also  of  the  heaviest  rainfall  that  occurs  in  shorter  periods  than 
a  day,  even  sometimes  in  fractions  of  an  hour.  Unfortunately 
it  is  not  likely  that  this  information  will  be  obtainable,  at  any 
rate  during  the  period  of  study  of  any  new  reservoir  project. 
So,  again,  it  will  be  better,  if  possible,  to  calculate  with  what- 
ever figures  may  be  obtainable  from  observations  on  the 
streams  by  which  the  flow-off  reaches  the  reservoir.  There 
may  be  a  record  of  discharges  kept ;  or,  if  there  is  no  such 
record,  discharges  may  be  taken  expressly  for  the  purpose  of 
the  reservoir  study.  The  residents  of  the  locality  may,  possibly, 
be  able  to  point  out  the  highest  marks  reached  at  different 
places  along  the  course  of  the  streams  by  the  greatest  flood 
known  to  them.  From  these  marks  the  surface  slope  of  the 
flood  can  be  ascertained,  and  with  the  gradient  thus  determined, 
and  with  cross-sections  of  tho  waterway  taken  opposite  the 
marks,  the  flood  discharges  can  be  calculated.  This  method 
of  estimating  the  maximum  discharge  which  flows  off  a  catch- 
ment will  give  more  reliable  results  than  calculations  based  on 
rainfall  statistics  and  an  assumed  value  for  the  proportion  of 
flow-off.  But  if  the  former  method  is  not  practicable,  the 
latter  must  be  followed  faute  de  mieux.  In  the  calculation  of 
the  maximum  flow-off,  the  time  occupied,  or  the  rate  of  flow, 
is  an  important  factor.  In  steep  and  barren  catchments  the 
rate  is  rapid,  and  the  total  flcw-off  arrives  in  the  reservoir  in  a 
shorter  time  than  it  does  from  catchments  of  gentle  slope  or 
wooded  surface.  Also  from  small  catchments  the  flow-off  is 


DAMS   AND  RESERVOIRS.  ftp 

rapid  relatively  to  that  of  large  catchments.  As  the  circum- 
stances of  every  case  differ  so  widely,  it  is  impossible  to  lay 
down  rules  for  calculating  what  discharging  capacity  should 
be  given  to  the  reservoir  escape.  The  peculiar  circumstances 
of  each  case  must  be  studied  and  the  allowance  determined  to 
the  best  of  one's  judgment.  Formulas  there  are  which  are 
used  in  India  to  work  out  what  discharge  per  square  mile  of 
drainage  area  the  reservoir  escape  should  provide  for,  but  the 
correctness  of  the  results  obtained  depends  altogether  on  the 
discretion  with  which  the  formula  is  used.  The  co-efficient, 
which  is  the  controlling  factor  of  the  formula,  varies  from  150 
to  1,000,  and  even  more.  The  use  of  any  of  the  formulas  does 
not  avoid  the  necessity  of  a  right  judgment  of  the  special 
conditions  affecting  the  particular  case  under  consideration. 
With  this  warning  the  formulas  most  commonly  used  are  given 
below.  In  both  of  them 

D  =  discharge  in  cubic  feet  per  second, 
M  =  area  of  catchment  in  square  miles, 
C  is  a  co-efficient. 

(1)  Dickens'  formula:  D  =  C  VW 

(2)  Ryves'  formula  :  D  =  C  V~W 

In  Madras,  Ryves'  formula  is  generally  used  with  the  following 
values  for  C  : — 

Within  15  miles  of  the  coast  —  450, 
Between  15  and  100  miles  from  the  coast  —  563. 
For  limited  areas  near  the  hills  . —  675. 

In  the  Bombay  Presidency  the  waste  weirs  of  tanks  and 
reservoirs  are  designed  to  discharge  from  212  to  967  cubic  feet 
per  second  per  square  mile  of  catchment,  the  allowance  varying 
with  the  amount  of  average  annual  rainfall,  with  the  area  of 
the  catchment,  and  with  the  slope  of  the  river  above  the  reser- 
voir. In  other  parts  of  India  the  discharge  which  the  reservoir 
escape  is  designed  to  pass  may  vary  between  150  and  600  cubic 
feet  a  second  per  square  mile  of  hill  areas,  and  between  25  and 
160  from  areas  in  the  plains.  But  there  is  a  case  of  a  tank  in 


70  IRRIGATION. 

* 

India,  fed  by  a  rocky  catchment  of  small  area,  in  which  the 
discharging  capacity  of  the  waste  weir  is  as  much  as  1,936  cubic 
feet  per  square  mile;  and  another  as  much  as  3,514  cubic  feet. 
The  latter,  if  not  also  the  former,  is  probably  in  excess  of 
requirements.  ' 

The  storage  capacity  of  the  reservoir  may  be  limited  by  the 
physical  features  of  the  site,  the  amount  of  flow-off  from  the 
catchment  that  can  be  relied  upon,  or  by  the  requirements  of 
the  land  to  be  irrigated.  As  a  rule  the  demand  is  greater  than 
the  maximum  supply  possible,  and  it  is  the  volume  of  the  flow- 
off  that  determines  what  capacity  should  be  given  to  the  reservoir. 
There  are  limits  to  the  height  to  which  it  is  safe  or  practicable 
to  build  dams  to  store  water,  and  the  configuration  of  the  ground 
maybe  such  that  no  reservoir  site  can  be  found  which  will  contain 
the  required  volume  of  storage  without  constructing  a  dam  of  a 
height  exceeding  the  maximum  permissible.  The  capacity  of 
the  Assuan  reservoir  in  Egypt  was  limited  for  exceptional 
reasons.  The  temples  on  the  island  of  Philae  had  worshippers 
whose  vigorous  protests  against  the  submersion  of  buildings 
which  some  of  them  had  never  seen,  resulted  in  the  dam  being 
built  at  first  to  a  height  26  feet  lower  than  was  originally 
intended.  The  capacity  of  the  reservoir  was  thus  reduced  from 
2,500,000,000  cubic  metres  to  i.ooc^ooOjOOO.1 

The  gross  capacity  of  a  reservoir  is  calculated  from  the  areas 
bounded  by  the  contours  between  the  high  water  level  of  the 
reservoir  and  the  reservoir  bed.  Its  "  available  capacity,"  or 
the  quantity  that  is  supplied  by  the  reservoir  through  its  outlet, 
is  the  volume  stored  between  the  high  water  level  and  the  sill 
of  the  outlet,  less  the  loss  due  to  evaporation  and  absorption  in 
the  reservoir  after  it  has  been  filled  and  replenishment  ceases. 

The  deduction  to  be  made  on  account  of  evaporation  depends 
upon  the  length  of  time  the  water  is  stored  after  the  final 
replenishment,  and  on  the  temperature  and  hygrometric  state 

1  The  subsequent  raising  of  the  dam  by  23  feet  has  increased  the  capacity 
to  2,200,000,000  cubic  metres. 


DAMS  AND   RESERVOIRS.  71 

of  the  air  for  that  period.  Observation  alone  can  determine 
exactly  what  the  deduction  should  be.  There  is  also  a  loss 
from  leakage  and  absorption  depending  on  the  nature  of  the 
bed  of  the  reservoir.  It  may  be  taken  roughly  as  equal,  in  the 
year,  to  half  that  due  to  evaporation.  The  loss  due  to  evapora- 
tion in  a  year,  measured  in  vertical  height,  may  vary  from 
3  to  10  feet,  according  to  the  climatic  conditions. 

The  dam,  which  is  the  principal  feature  of  a  reservoir  project, 
may  be  made  of  earth  or  of  masonry,  or  of  a  combination  of 
both.  There  are  dams  of  a  type  peculiar  to  America  known 
as  "  rock-fill  "  and  "  loose  rock  "  dams.  They  are  formed  of  a 
mass  of  rubble  with  a  water-tight  facing,  which  may  be  of 
planks,  of  asphalt  or  Portland  cement  concrete,  of  masonry, 
of  steel  plates,  or  of  earth.  Another  type  peculiar  to  America 
is  a  dam,  either  of  earth  or  loose  stone,  with  a  central  core  of 
steel  plates  forming  a  water-tight  diaphragm  embedded  in  the 
mass  of  the  dam. 

Masonry  dams  may  be  classified  as — 

(a)  Solid  submergible  dams,  over  the  crest  of  which  the 
discharge  passes ; 

(6)  Solid  insubmergible  dams,  with  waste  weirs  to  discharge 
excess  water,  and  outlets  for  the  delivery  of  the  stored  water; 

(c)  Insubmergible    dams,    pierced    with    numerous   sluices, 
through  which  the  discharge  is  passed. 

Earthen  dams  must  always  be  insubmergible,  and  be  pro- 
vided with  waste  weirs  and  outlets.  They  may  be  divided  into 
three  classes,  namely, — 

(d)  Dams  with  masonry  core  walls  ; 

(e)  Dams  with  central  puddle  core ; 

(/)  Dams  entirely  of  earth  without  core  walls. 

The  question  as  to  which  class  of  dam  is  the  most  suitable 
for  any  particular  site  depends  to  a  great  extent  on  the  nature 
of  the  foundation.  k  A  high  masonry  dam  must  have  sound  rock 
for  its  foundation.  This  is  a  sine  qua  non.  An  earthen  dam 
may  be  built  on  sandy  or  gravelly  clay,  fine  sand  or  loam,  and 


/2  IRRIGATION. 

also  on  rock  if  proper  precautions  are  taken  to  prevent  creep  of 
water  between  the  bed  of  the  dam  and  the  rock  surface. 
Earthen  dams  can  be  safely  built  up  to  75  feet  in  height, 
though  French  engineers  fix  the  safety  limit  at  60  feet.  No 
doubt  60  feet  is  a  safer  limit  than  any  greater  height,  but  there 
are  earthen  dams  in  India,  exceeding  75  feet  in  height,  which 
have  now  been  tested  by  many  years  of  useful  work.  There 
are  in  existence  also  earthen  dams  of  80  and  100  feet  in  height, 
and  one  of  even  125  feet.  Mr.  Strange  considers  that  embank- 
ments above  75  feet  in  height  should  be  reinforced  by  adding 
dry  stone  toes  to  the  slopes,  and  that,  with  this  addition,  dams 
might  be  safely  constructed  up  to  125  feet  in  height.  He 
admits,  however,  that  when  a  height  of  60  feet  is  exceeded 
particular  care  must  be  taken  both  with  the  design  and  with 
the  construction. 

The  choice  between  earth  and  masonry  for  the  dam  construc- 
tion is  affected  also  by  economical  considerations,  and  the 
f actilities  for  transporting  materials  to  the  site  of  the  work. 

As  earthen  dams  are  doubtless  of  earlier  origin  than  masonry 
dams,  they  will  be  considered  first. 

The  design  and  construction  of  earthen  dams  has  been  treated 
fully  by  Mr.  W.  L.  Strange  in  his  practical  treatise  on  "  Indian 
Storage  Reservoirs  with  Earthen  Dams  "  (1913),  from  which 
much  of  what  follows  relating  to  them  is  borrowed. 

The  design  of  an  earthen  dam  includes  the  dam  proper,  the 
waste  weir,  and  the  delivery  outlet.  The  safest  arrangement  is 
when  each  of  these  three  works  are  separate  one  from  the  other, 
the  waste  weir  being  on  one  side  of  the  dam  and  the  outlet  on 
the  opposite  side.  But  for  the  sake  of  economy,  or  other 
reasons,  they  'are  often  combined  in  one  work.  The  more 
common  arrangement  is  to  combine  the  dam  and  outlet  in  one 
work,  and  to  separate  the  waste  weir.  If  the  three  works  are 
separate,  and  there  is  no  outlet  passing  through  the  dam,  it  is 
probably  best  to  construct  the  dam  entirely  of  earth  of  the 
same  character  throughout,  the  soil  selected  being  of  a  descrip- 


DAMS  AND   RESERVOIRS.  73 

tion  that  is  impervious  and  stable  under  the  action  of  water. 
The  cross  section  of  such  a  dam  of  ordinary  good  soil,  if  from 
50  to  75  feet  in  height,  should  have  the  following  dimensions: — 
The  crest  of  the  dam  should  be  6  or  7  feet  above  the  high 
water  level  of  the  reservoir;  the  crest  width  should  be  10  feet ; 
the  up-stream  slope  on  the  reservoir  side  should  have  3  of 
base  to  I  of  rise,  and  the  down-stream  slope  2  to  i.  If 
the  dam  is  15  feet  high  or  under,  the  crest  of  the  dam  may 
be  4  to  5  feet  above  high  water  level,  the  top  width  6  feet, 
up-stream  slope  2  to  i,  and  down-stream  ij  to  i.  For  dams  of 
heights  between  15  feet  and  50  feet  the  dimensions  may  be 
intermediate  between  the  foregoing. 

It  will  be  necessary  t$  protect  the  up-stream  slope  between  low- 
water  level  and  high-water  level  with  a  skin  of  dry  rubble  revet- 
ment, or  of  some  other  suitable  material,  to  resist  the  erosive 
action  of  the  waves  of  the  reservoir;  and  the  down-stream 
slope  also  must  be  so  clothed  as  not  to  be  guttered  by  rainfall. 

The  reinforcement  of  the  slopes  of  earthen  dams  of  more 
than  75  feet  height  by  the  addition  of  dry  stone  toes  is  desirable 
to  give  security  against  sliding.  The  down-stream  stone  toe  is 
also  useful  in  providing  for  the  drainage  of  the  heart  of  the 
dam  without  injury  to  the  down-stream  face,  and  is,  on  this 
account,  preferable  to  the  solid  masonry  retaining  wall  which 
has  been  added  to  some  dams  as  a  support  to  the  down-stream 
slope.  The  Maladevi  Tank  dam  l  in  Bombay  was  designed  as 
an  earthen  dam  with  dry  stone  toes.  At  its  highest  point  it  is 
subjected  to  a  water  pressure  of  98  feet.  Its  up-stream  and 
down-stream  slopes  are  3  to  i  and  2  to  i  respectively,  but 
these  slopes  change  above  high-water  level.  The  up-stream 
face  above  high-water  level  is  protected  by  a  crest  wall  of 
masonry  with  a  batter  of  J  to  i,  the  down-stream  slope  changing 
to  1 1  to  i.  The  up-stream  wall  of  masonry  protects  the  crest 
from  wave- wash,  acting  as  a  breaker.  It  also  prevents  burrowing 
animals  from  injuring  the  dam. 

1  The  Maladevi  Tank  dam  was  not  built,  another  site  having  been  preferred. 


74  IRRIGATION. 

In  the  construction  of  earthen  dams,  particular  attention 
must  be  given  to  the  foundations.  Not  only  must  precautions 
be  taken  to  prevent  creep  of  water  between  the  natural  ground 
and  the  artificial  earthwork  of  the  dam,  but  provision  must  be 
made  for  intercepting  any  percolation  water  that  may  travel 
through  the  subsoil,  or  for  leading  it  harmlessly  away.  Also, 
to  prevent  the  dam  itself  becoming  saturated  and  consequently 
slipping  or  subsiding,  it  is  necessary  either  to  guard  against  the 
water  entering  the  dam,  or  to  provide  means  of  getting  rid  of  it 
if  it  does  enter.  Thorough  drainage  of  the  earthwork  and  of  its 
foundations  is,  therefore,  the  condition  essential  to  security.  To 
the  endeavour  to  exclude  the  water  from  the  dam,  cut  off  the  creep 
at  or  below  foundation  level,  and  provide  drainage  for  the  dam  and 
its  foundations,  the  different  types  of  earthen  dams  are  due. 

The  first  condition  for  the  adoption  of  an  earthen  dam  in  a 
storage  project  is  that  the  soil  of  the  foundations  and  that  for 
the  construction  of  the  dam  itself  must  be  suitable,  the  one  to 
withstand  the  weight  of  the  dam,  and  the  other  to  resist  the 
passage  of  water  and  any  tendency  to  saturation. 

Borings  into  the  foundation,  or  trial  pits,  will  reveal  the 
nature  of  the  subsoil  and  furnish  the  information  necessary  for 
determining  the  measures  to  adopt  in  each  case.  If  the  sub- 
soil is  porous  (and  most  subsoils  are  more  or  less),  or  if  it  is  of 
rock  with  porous  seams,  the  usual  course  is  to  make  a  puddle 
trench  under  the  centre  of  the  dam  to  offer  a  water-tight 
obstacle  to  the  movement  of  the  water,  so  that  all  down  stream 
of  it  may  be  kept  dry.  The  bottom  width  of  this  curtain  should 
not  be  less  than  6  feet  for  small  dams,  nor  less  than  10  feet 
for  high  dams.  The  usual  rule  is  to  make  the  base  width  equal 
to  one-quarter  of  the  full  supply  depth  of  the  reservoir  at  any 
given  point.  The  depth  of  the  puddle  trench  will  depend  upon  the 
porosity  of  the  soil  and  the  head  of  water  in  the  reservoir,  and 
may  vary  from  half  the  depth  to  the  whole  depth  of  the  full 
supply  storage  in  the  reservoir,  or  more.  The  trench  must 
be  carried  down  until  it  enters  for  2  feet  at  least  into  good 


DAMS   AND   RESERVOIRS.  75 

clayey  soil  extending  downwards.  Or,  if  rock  is  met  with 
before  reaching  these  depths,  the  trench  should  be  carried  at 
least  i  foot  down  into  the  rock  to  form  a  good  joint  with  it. 
If  sandy  and  highly  porous  layers  exist  to  a  great  depth,  it  may 
be  necessary  to  condemn  the  site  and  give  up  the  project. 

To  cut  off  the  creep  between  the  natural  ground  and  the 
artificial  bank  above  it,  the  puddle  filling  of  the  trench  should 
be  continued  upwards  past  the  plane  of  junction  for  a  foot  or 
more,  so  as  to  make  a  bond  with  the  earthwork  of  the  dam. 
The  foundation  of  the  dam  should  also  be  benched  to  present 
surfaces  for  the  dam  to  rest  on  slightly  inclined  towards  the 
centre  of  the  dam.  Along  the  bottom  angles  of  this  benching 
which  are  up  stream  of  the  main  puddle  trench,  small  puddle 
trenches  should  be  formed  parallel  to  the  main  trench,  and  along 
the  angles  of  the  down-stream  benching  trenches  should  be 
made  and  filled  with  porous  material  to  serve  as  foundation 
drains.  In  the  design  of  the  Maladevi  Tank  dam,  where  it  rests 
upon  rock,  concrete  walls,  sunk  in  the  rock  surface,  take  the 
place  of  the  puddle  curtain  barrier. 

But,  if  the  material  of  the  dam  is  not  absolutely  water-tight, 
water  will  find  its  way  through  the  mass  of  the  dam  to  the 
down-stream  face,  possibly  to  a  dangerous  extent.  To  provide 
against  this,  the  puddle  trench  has  been  sometimes  developed 
into  the  puddle  core  by  carrying  up  the  puddle  as  a  thin  wall, 
in  continuation  of  the  puddle  in  the  foundation  trench,  from 
the  bottom  of  the  dam  to  above  high  water  level.  By  this 
means  the  penetration  of  water  into  the  mass  of  the  dam  is 
confined  to  the  half  of  it  up  stream  of  the  puddle  wall,  and  the 
stability  of  the  down-stream  half  is  not  affected  by  any  soakage. 
Regarding  the  dimensions  to  be  given  to  puddle  walls  opinions 
differ,  but  Rankine's  rule  is  that  the  thickness  at  the  base  should 
be  about  one-third  of  the  height,  and  the  thickness  at  the  top 
two-thirds  or  one-half  that  of  the  base. 

The  objection  to  a  puddle  core  is  that  it  is  liable  to  rupture 
from  unequal  settlement  of  the  earthwork  of  the  dam,  and  it 


76 


IRRIGATION. 


then  ceases  to  be  water-tight.  For  this  reason,  masonry  core 
walls  are  to  be  preferred,  though,  generally  speaking,  their  cost 
would  be  considerably  greater.  But  a  masonry  core  wall 
requires  solid  and  sound  rock  for  its  foundation,  and  therefore 
cannot  take  the  place  of  a  puddle  core  unless  this  condition  is 
fulfilled.  If  the  waste  weir  or  outlet,  or  both,  are  combined 
with  the  dam  in  one  work,  the  masonry  core  wall  adds  con- 
siderably to  the  security,  as  it  enables  a  perfectly  sound  bond 

CROTON      DAM 


EARTHEN     LENGTH 


FIG    7 


W.L.  tee 


Scale     of 


to  be  made  between  the  dam  and  its  associated  works.  This 
is  important,  as  an  outlet,  for  instance,  passing  through  an 
earth  dam  without  a  masonry  core  wall,  is  always  a  source  of 
weakness,  offering  a  line  for  leakage  if  there  should  have  been 
anything  defective  either  in  design  or  execution. 

Whether  the  core  be  of  puddle  or  masonry,  it  must  be  con- 
tinued outwards  to  both  flanks  up  to  high  water  level,  the  changes 
of  level  in  the  foundation  bed  of  the  core  at  the  flanks  being 
effected  by  vertical  rises.  Great  care  must  be  taken  to  form  a 
good  bond  between  the  dam  and  its  natural  abutments  lest  a 
leak  should  form  between  the  two.  Opinions  differ  also  as  to 
the  dimensions  that  should  be  given  to  masonry  cores.  The 
earthen  length  of  the  New  Croton  dam,  New  York,  is  con- 
sidered to  be  of  good  design  (Fig.  71).  It  has  a  masonry  core 


1  The  earthen  length  after  partial  construction  was  altered  to  a  solid 
masonry  dam. 


DAMS  AND    RESERVOIRS. 


77 


which  is  carried  down  to  a  depth  of  125  feet  below  the 
surface ;  for  89  feet  from  its  foundation  level  it  has  a  width  of 
18  feet,  and  thence  it  gradually  decreases  to  a  top  width  of 
6  feet  at  a  level  14  feet  below  the  crest.  This  dam  has  a 
height  of  120  feet  above  the  original  ground  surface.  It  abuts 
on  to  another  length  of  dam  in  masonry. 

The  position  of  the  water-tight  component  of  a  dam  in  the 
centre  of  the  embankment  is  theoretically  an  unfavourable  one. 
The  water  enters  the  up-stream  half  of  the  dam  and  reaches  the 


FOY    SAGAR    TANK     DAM 


feet 


core  wall.  It  is  thus  the  impermeable  core  wall,  backed  up 
by  the  down-stream  half  of  the  dam,  which  does  all  the  retaining 
work.  The  up-stream  half  is  only  useful  in  preventing  the  wall 
from  falling  inwards  towards  the  reservoir  when  the  latter  is 
empty.  So  dams  of  a  section,  such  as  that  of  the  Foy-Sagar 
Tank  (Fig.  8),  would  appear  to  answer  all  the  purposes  of  a 
full-section  earth  dam,  provided  the  wall  is  strong  enough  to 
hold  up  its  backing  when  the  reservoir  is  empty,  r  The  dimen- 
sions of  the  face  wall  of  the  Foy-Sagar  Tank  dam  are  certainly 
remarkably  light,  and  are  even  less  than  those  of  the  core  wall 
of  the  Kair  Tank  dam  (Fig.  9)  which  has  a  support  of  earth 
on  both  sides. 


/8  IRRIGATION. 

In  consequence  of  the  theoretical  objection  to  the  situation 
of  the  impermeable  diaphragm  in  the  centre  of  the  mass,  a 
puddle  surface  has  sometimes  been  given  to  the  reservoir  face 
of  the  dam  to  prevent  the  water  from  entering  the  bank  at  all. 
But  there  is  a  practical  drawback  to  this  arrangement  which 
has  caused  its  rejection :  the  puddle  is  liable  to  slide  and  crack 
when  the  water  level  in  the  reservoir  is  low  or  the  embankment 
settles,  and  so  to  be  no  longer  water-tight.  The  puddle  core 
in  the  centre  of  the  dam,  on  the  other  hand,  is  protected,  by 
reason  of  its  position,  from  the  effects  of  the  weather,  and  has 
no  tendency  to  slide  or  crack,  so  that  it  is  more  likely  to  remain 

KAfR     TANK      DAM 

Scalg  FIG      9 

10  6    0        to       80       30       40       60 

Nl         I         I         I         I         I 


Feet 


water-tight.  But  with  a  masonry  core  wall  this  argument  does 
not  apply,  and  the  up-stream  half  of  the  dam,  as  has  been 
stated,  only  serves  to  support  the  wall  when  the  reservoir  is 
empty.  As  a  masonry  core  wall  cannot  be  built  except  on 
rock  foundations  such  as  would  be  suitable  for  a  masonry  dam, 
it  would  be  a  matter  for  consideration  whether,  instead  of  an 
earth  dam  with  a  masonry  core  or  face,  it  would  not  be  better 
to  substitute  a  masonry  dam. 

There  seems  to  be  a  growing  tendency  to  prefer  one  of  the 
two  extremes,  either  an  earthen  embankment  of  uniform  section 
and  homogeneous  material  without  any  core  wall,  or  a  dam 
wholly  of  masonry.  Between  these  two  extremes  lie  all  the 
composite  varieties  of  dams.  It  is  possible  that  one  or  other 
of  the  varieties  may  be  found  more  suited  to  the  special 


DAMS   AND   RESERVOIRS.  79 

conditions  of  a  particular  site  than  the  all-earth  or  all-masonry 
dam  would  be. 

Dams  of  the  American  type  form  a  class  by  themselves.  The 
dam  with  a  central  water-tight  diaphragm  of  steel  plates,  how- 
ever, belongs  to  the  class  of  dams  with  masonry  or  puddle 
cores,  as  its  principle  of  action  is  the  same.  It  differs  only  as 
regards  the  material  of  which  the  dam  is  made  in  those  cases 
in  which  dry  rubble  is  substituted  for  earth  to  form  the  mass  of 
the  dam  on  either  side  of  the  core.  The  steel  plate  is  embedded 
in  a  concrete  base  forming  a  junction  with  the  bed-rock.  In 
such  a  dam  the  principle  is  recognised  that  the  core  alone  stops 
the  passage  of  water,  and  the  material  on  either  side  of  it 
merely  acts  as  a  support  to  enable  it  to  resist  the  pressure. 
Instances  of  this  class  of  dam  are  to  be  found  in  Southern 
California. 

"  Loose-rock  "  dams  are  simply  dams  made  of  dry  rubble 
with  an  impervious  up-stream  face  of  tarred  planking  or  earth. 
The  safe  section  for  this  class  of  dam  is  not  much  less  than 
that  of  an  earthen  dam :  the  upper  and  lower  slopes,  however, 
can  be  made  steeper  than  those  of  an  earthen  dam ;  but  2  to 
i  for  the  upper  slope  and  i  to  i  for  the  lower  is  as  steep 
as  they  should  be  made.  A  facing  of  earth,  supported  by  loose 
rubble  below  water,  is  not  a  good  disposition  of  material. 
Wood  also,  being  perishable,  is  not  a  good  material  for  use 
in  a  permanent  structure.  So  this  type  of  dam  is  not  in  favour, 
nor  is  it  likely  to  be. 

The  "  rock-fill  "  dam  is  made  ol  a  mass  of  loose  rubble 
with  a  front  and  back  wall  of  masonry  forming  steep  sloping 
faces.  On  the  upper  face  there  is  sometimes  added  a  covering 
of  two  thicknesses  of  planking  with  tarred  paper  between,  the 
joints  of  the  outer  planks  being  caulked  and  the  whole  face 
painted.  The  "Walnut  Grove"  dam,  built  in  this  way,  had 
a  greatest  height  of  no  feet.  It  was  topped  and  destroyed  by 
a  flood  in  1890,  the  waste  weir  proving  insufficient  for  its 
purpose.  The  dam  of  the  Castlewood  reservoir  in  Colorado, 


8o 


IRRIGATION. 


another  of  this  type,  still  exists  as  the  only  specimen  of  its 
class.  Its  section  is  given  in  Fig.  10.  This  kind  of  dam  may 
be  classed  with  the  composite  masonry  and  earth  dams  of  the 
Foy-Sagar  variety  (Fig.  8),  dry  rubble  taking  the  place  of  the 
earth  backing  and  acting  as  a  support  to  the  face  wall  in  the 
same  way. 

Such  dams  as  "  locse-stone "  and  "rock-fill"  are  of  an 
inferior  class  to  the  all-masonry  dam.  The  masonry  dam, 
founded  on  sound  rock,  has  fewer  weak  points  in  its  constitu- 
tion than  other  forms,  and  for  certain  situations  is  the  only 

CASTLEWOOD     RESERVOIR     DAM 


W.L.  f»  Reservoir 


form  that  could  stand.  Nothing  but  a  masonry  dam,  for 
instance,  would  have  been  possible  for  the  Assuan  dam  on 
the  Nile.  Examples  of  the  three  classes  of  masonry  dams — 
the  submergible,  the  solid  insubmergible,  and  the  pierced  in- 
submergible — are  given  in  Figs,  n  to  22,  25,  and  26.  A 
selection  has  been  made  from  among  dams  of  recent  con- 
struction, as  embodying  the  ideas  of  modern  engineering 
concerning  the  design  of  high  masonry  dams,  so  far  as  recent 
work  affords  examples.  The  main  dimensions  of  these  dams 
are  shown  on  the  figures,  and  they  will  therefore,  as  a  rule, 
not  be  given  in  the  text. 

The  variety  in  design  of  existing  dams  is  great,  but  in  the 


DAMS  AND   RESERVOIRS.  8 1 

high  dams  constructed  during  recent  years  there  is  a  tendency 
to  uniformity  of  design  where  the  conditions  are  similar.  This 
is  no  doubt  the  result  of  a  general  acceptance  of  the  theory  of 
stresses  in  dams,  which  mathematical  investigators  had,  till 
quite  lately,  held  to  be  sound.  The  soundness  of  the  theory, 
on  which  the  design  of  most  modern  dams  has  been  based,  has 
now  been  called  in  question  and  is  being  put  to  the  test. 

The  forces  acting  on  a  dam  are — (i)  the  pressure  of  the 
water  in  the  reservoir  exerted  in  a  direction  at  right  angles  to 
the  up-stream  face  and  (2)  the  weight  of  the  dam  itself  acting 
vertically. 

In  a  masonry  dam  the  conditions  of  stability,  as  commonly 
accepted,  are  three,  namely, — 

(1)  The  lines  of  pressure,  both  when  the  reservoir  is  full  and 
when  it  is  empty,  must  lie  within  the  centre  third  of  the  cross- 
section  ; 

(2)  The  pressures  in  the  masonry  or  on  the   foundations 
must  never  exceed  safe  limits  ; 

(3)  The  friction  between  the  dam  and  its  foundation  bed,  or 
between  any  two  parts  into  which  the  dam  may  be  divided, 
must  be  sufficient  to  prevent  sliding. 

Compliance  with  the  first  condition  gives  security  against 
overturning.  Until  lately  it  we  s  assumed  that  it  also  precluded 
the  possibility  of  tensile  stresses  on  the  masonry.  But  the 
justification  for  this  assumption  is  now  questioned,  and  it  is 
contended  that,  if  the  dam  is  treated  as  an  elastic  solid,  it  is 
necessary  to  take  account  of  the  elastic  shear  as  well  as  the 
elastic  compression.  Mr.  Atcherley  holds  that  it  is  not  suffi- 
cient to  consider  the  stresses  in  horizontal  sections,  but  the 
stresses  in  vertical  sections  also  must  be  investigated,  and  it 
will  then  be  found  that  tensions  exist  in  the  toe  of  the  dam  to  an 
extent  that  cannot  be  disregarded.  Sir  Benjamin  Baker,1  after 
discussion  of  this  question,  and  admitting  that  tension  in 
masonry  should  be  avoided  as  far  as  possible,  expressed 
1  Vol.  CLXII.  "  Proceedings  Inst.  C.E.,"  pp.  120,  456. 

I.  G 


82  IRRIGATION. 

his  opinion  that,  "  whatever  theory  mathematicians  might 
evolve,  engineers  would  not  be  relieved  from  the  obligation 
to  use  no  materials  for  dams  which  would  not  stand,  say, 
fifty  tons  per  square  foot  in  compression  and  ten  tons  per 
square  foot  in  tension  without  splintering."  In  existing  dams 
the  actual  maximum  pressures  vary  as  a  rule  from  six  to 
fourteen  tons  per  square  foot. 

In  practice  it  is  found  that  if  the  above  conditions  (i)  and  (2) 
are  satisfied,  so  also  is  condition  (3). 

Masonry  dams   of  great   height   were   first  built  in  Spain. 


H.W.L. 


BETWA      DAM 


10    50        ao      20       30      40 


The  Alicante  dam,  of  140  feet  greatest  height,  was  built 
between  the  years  1579  and  1594;  but  the  Almanza  dam, 
68  feet  high,  was  built  at  some  unknown  date  long  before. 
Nearly  all  the  dams  of  Spain  are  built  across  mountain  gorges 
on  rock  foundations. 

The  construction  of  the  Furens  dam  in  France,  between  the 
years  1862  and  1866,  marks  the  next  great  advance  in  dam- 
building.  The  French  engineers  were  the  first  to  work  out 
the  scientific  principles  according  to  which  dams  should  be 
designed,  and  to  test  their  soundness  by  applying  them  to 
actual  practice.  The  Furens  dam,  of  a  greatest  height  of 


DAMS    AND   RESERVOIRS.  83 

177  feet  from  foundation  to  crest,  was  the  first  dam  to  which 
these  principles  were  applied.  Its  section  is  given  in  Fig.  17. 
It  belongs  to  the  insubmergible  class. 

Submergible  dams,  of  which  examples  are  given  in  Figs.  II 
to  16,  exhibit  heavier  profiles  relatively  to  the  height  of  the 
dam  than  those  which  are  insubmergible.  The  submergible 
dams  act  as  overflow  weirs,  and  have  to  support  the  extra 

LA    GRANGE    DAM 


Scale 

10        0        10      20       30       40      60 

'          ' 


pressure  due  to  the  depth  of  water  which  flows  over  their  crests, 
and  also  to  resist  the  action  of  falling  water  on  the  down-stream 
side.  Many,  if  not  most,  of  the  dams  that  belong  to  this  class 
have  subsidiary  weirs  associated  with  them.  These  weirs  are 
built  in  the  channel  some  distance  down  stream  of  the  main  dam 
with  the  object  of  holding  up  the  water  above  them  to  form  a 
pond  or  water-cushion  on  which  the  falling  water  may  expend 
its  force.  The  toe  of  the  dam  and  the  rock  adjacent  is  thus 

G2 


84 


IRRIGATION* 


protected  from  scouring  action.  The  Betwa  dam,  in  India, 
(Fig.  n)  has  a  solid  platform  of  masonry  for  its  down-stream 
toe,  the  upper  surface  of  which  is  submerged  10  feet  by  the 
water  ponded  up  by  a  subsidiary  weir  18  feet  in  height.  The 
shock  of  the  falling  water,  moderated  by  the  water-cushion,  is 
thus  borne  by  the  solid  projecting  platform. 

VYRNWY     DAM 


&*» 

'?  6  9      IP      ,       .— -        30 


Fee* 


The  Turlock,  or  La  Grange  dam,  in  California,  (Fig.  12) 
has  similarly  a  subsidiary  weir,  20  feet  high,  situated  200 
feet  from  the  main  dam.  But  it  has  no  platform  down 
stream,  and  its  cross-section  differs  greatly  from  that  of 
the  Betwa  Dam.  The  Turlock  profile  is,  however,  the 
more  common  form  of  the  two,  and  is  typical  of  a  large 
number  of  existing  submergible  dams.  The  Turlock  dam 


DAMS   AND   RESERVOIRS. 


is  designed  for  a  maximum  depth  of  16  feet  of  water  flowing 
over  its  crest. 

The  cross-section  of  the  Vyrnwy  dam,  in  Wales,  (Fig.  13) 

CROTON      DAM 


MAXIMUM    SECTION     OF 
SUBMERGIBLE    LENGTH 

Scale 


FIG      14 

196 


HENARES      WEIR 


Scale      v 
to  IB  *       so  \       n 

1  '  ' 


so 


Fett 


R     O 


exhibits,  though  in  not  a  very  pronounced  form,  the  ogee 
down-stream  face.  There  is  a  cushion  of  45  feet  depth  of  water 
over  its  toe.  The  force  of  the  falling  water  is,  moreover, 
broken  up  during  its  descent  over  the  down-stream  face  by  the 


86 


IRRIGATION. 


roughness  of  the  surface.  Very  large  stones  were  available  for 
the  building  of  this  dam,  and  were  used  in  the  down-stream  face 
with  the  roughest  possible  exposed  surfaces.  In  consequence 
of  this  arrangement  the  overflow,  according  to  the  description 
given  by  Dr.  Deacon,  reaches  the  pool  below  as  "  white  spray  " 
instead  of  as  "  solid  water,"1  the  force  of  its  fall  being  expended 
on  the  rough  projecting  surfaces  of  the  down-stream  face  stones. 
This  is  as  it  should  be.  It  is  a  mistake,  sometimes  made,  to  adopt 
the  ogee  curve  for  the  down-stream  face  and  to  make  the  surface 
smooth.  With  such  an  arrangement  the  water  glides  evenly 


VIR    NALA    DAM 

Scale 


£ 


FIG     16 

60 


M 


H.W.L. 


46.365- -.4.-.. .-.<<-*** 


over  the  crest  and  down  the  slope  of  the  dam  with  a  delusively 
harmless  appearance.  But  the  less  resistance  the  water  meets 
with  during  its  descent,  the  greater  will  be  its  velocity  and  its 
power  to  work  mischief  on  its  arrival  at  the  toe.  The  mistake 
was  made  in  India  on  the  Ganges  canal  when  it  was  first 
constructed.  %  The  weirs  were  originally  given  ogee  profiles,  but 
they  have  since  been  converted  into  stepped  weirs,  or  weirs  with 
vertical  drops,  so  as  to  prevent  excessive  horizontal  velocity. 

The  Henares  weir,  in  Spain,  has  the  ogee  form  (Fig.  15).     It 
should  be  classed,  perhaps,  as  a  river  regulator  rather  than  a 
»  Proceedings  Inst.C.E.,  Vol.  CLXIL,  p.  no. 


DAMS    AND   RESERVOIRS.  87 

submergible  dam  ;  or  it  may  be  considered  an  intermediate  type 
between  the  Indian  anicut  and  a  dam  of  the  Turlock  form.  It 
is  founded  on  rock  which  has  sufficient  strength  to  resist  the 
action  of  the  high  velocity  current  acquired  by  the  water  in  its 
unimpeded  passage  from  above  to  below  the  weir. 

The  canal  head-works  at  Vir  Wadi  on   the  Nira  river  in 
India   include  a  dam  which  is    a   combination    of  two  weirs, 

FURENS     DAM 


10    0    10  60  1QO 

Scale  of  Idiiiil     I     I     I     IT    I     I     I     I    I   Feet 


made  up  of  a  main  weir  across  both  the  Nira  river  and  the  Vir 
Nala  and  a  subsidiary  weir  down-stream  on  either  channel. 
Both  weirs  are  founded  on  rock.  The  subsidiary  weir  on  the 
Nira  river  is  over  1,000  feet  distant  from  the  main  weir,  but 
that  across  the  Vir  Nala  (Fig.  16)  is  only  about  40  feet  distant. 
The  objection  to  such  an  arrangement  as  that  shown  in  Fig.  16 
is  that  boulders  may  get  imprisoned  between  two  weirs  so  near 
together  and,  under  the  action  of  currents  and  eddies,  may  work 


88  IRRIGATION. 

deep  pot-holes  in  the  rock  bed  at  the  toe  of  the  main  weir. 
This  combination  of  weirs  should  be  classed  with  the  Henares 
weir  as  intermediate  between  a  river-regulating  weir  and  a 
submerged  dam.  It  acts  as  both. 

The  highest  submergible  dam  in  existence  is  that  of  Mun- 
daring,  in  Australia.     It  has  a  greatest  height  of  190  feet  from 

PERIYAR     DAM 


Scale 

TIII  T 


Feet 


foundation  to  crest,  which  latter  is  100  feet  above  the  original 
surface  of  the  ground.  It  is  designed  for  a  depth  of  overflow 
of  5  feet.  In  August,  1904,  there  was  an  overflow  of  18  inches, 
the  actual  maximum  up  to  that  date. 

Of  the  examples  of  solid  insubmergible  dams  given  in  Figs.  17 
to  22,  the  Furens  dam  has  already  been  referred  to. 

The  Periyardam,  in  India,  (Fig.  18)  forms  the  most  important 


DAMS   AND   RESERVOIRS. 


«9 


feature  of  the  irrigation  scheme  to  which  reference  was  made 
in  the  preceding  chapter  as  furnishing  an  illustration  of  the 
diversion  of  the  water  of  one  catchment  for  use  in  another. 
The  dam  is  built  in  a  narrow  rocky  gorge  269  feet  wide  at  the 
bed  and  1,241  feet  wide  at  the  parapet  level  of  the  dam.  The 
reservoir  came  into  operation  in  1896. 

MARIKANAVE    DAM 


Scale 


10    o    1,0 


Fttt 


fIG     19 


128- 


The  Marikanave  dam,  in  India,  (Fig.  19)  is  also  built  in  a 
gorge,  which  is  1,200  feet  broad  at  the  dam  crest  level.  The 
reservoir  formed  by  it  is  the  largest  in  India,  and  has  a  gross 
capacity  exceeding  that  of  any  other  reservoir  in  the  world, 
excepting  only  the  Assuan  reservoir  on  the  Nile.  Its  water- 
spread  is  34  square  miles,  and  maximum  capacity  30,000,000,000 
cubic  feet.  The  storage  capacity  of  the  reservoir  is,  however, 


90  IRRIGATION 

greatly  in  excess  of  the  calculated  annual  replenishment,  so  that 
it  is  not  expected  to  nil  more  than  once  in  six  years.  It  was 
for  economical  reasons  that  the  dam  was  given  the  extra  height 
which  has  provided  the  excess  storage.  xSir  Thomas  Higham 
has  explained  how  such  a  proceeding  could  result  in  economy. 
"  The  average  annual  rainfall  is  not  more  than  25  inches, 

CROTON      DAM 

INSUBMERGIBLE     LENGTH 

,       „  FIG     20 

ov 


Restored  Surface 
RiverBed 


and  the  inflow  due  to  such  a  fall  will  probably  not  exceed 
10,000,000,000  cubic  feet.  In  some  years  it  may  be  less,  or 
even  nil.  It  was  originally  proposed  to  provide  a  capacity  of 
20,000,000,000  cubic  feet,  which  would  about  equal  the  inflow 
due  to  an  annual  rainfall  of  30  inches  ;  but  there  were  records 
of  cyclonic  rainfalls,  the  run-off  of  which  would  not  only  fill  a 

1  "  Irrigation,''  Transactions  American  S.C.E.,  1904. 


DAMS  AND   RESERVOIRS.  QI 

tank  of  this  capacity,  but  would  also  require  an  overflow  capacity 
of  60,000  cubic  feet  a  second.  Such  an  escapage  could  only  be 
provided  by  cutting  a  deep  channel  of  adequate  dimensions 
through  hard  rock,  and,  as  a  matter  of  arithmetic,  it  was  found 
to  be  cheaper  to  increase  the  height  of  the  dam,  and  to  place 
the  bed  of  the  escape  at  a  higher  level." 

The  New  Croton  dam,  which  was  substituted  for  the  proposed 
Quaker  Bridge  dam,  has  been  constructed  to  impound  water  for 
the  supply  of  the  city  of  New  York.  Like  the  Titicus  dam,  it 
is  made  up  of  three  sections  which  furnish  illustrations  of  the 
earth  dam  with  masonry  core  (Fig.  7),  of  the  submergible 
masonry  dam  (Fig.  14),  which  serves  as  the  waste  weir  or 
overfall  to  the  reservoir,  and  of  the  solid  insubmergible  masonry 
dam  (Fig.  20).  The  insubmergible  length  has  a  height  of 
300  feet  at  the  point  where  the  foundations  are  lowest,  a 
height  which  would  have  been  considered  extreme  not  many 
years  ago.1 

The  above-mentioned  insubmergible  masonry  dams,  chosen 
as  typical  examples,  are  all  either  built  on  straight  alignments 
or  on  a  curvilinear  trace  so  flat  as  to  be  considered  straight  in 
calculating  the  dimensions  of  the  dam.  The  Furens  dam,  for 
instance,  has  a  curvature  of  827  feet  radius,  but  its  profile  was, 
nevertheless,  designed  as  if  for  a  straight  dam.  There  are  a 
few  dams,  closing  narrow  gorges,  which  depend  for  their 
stability  on  the  fact  that  they  are  built  to  a  curved  plan  which 
brings  into  play  the  principles  of  the  arch.  The  outer  ends  of 
these  dams  abut  on  the  rocky  flanks  of  the  gorge,  to  which  the 
water  pressure  is  transmitted.  The  transverse  dimensions  of 
the  dam  can,  therefore,  be  reduced  considerably,  and  it  is  no 
longer  a  necessary  condition  of  stability  that  the  line  of  pressure 
when  the  reservoir  is  full,  must  lie  within  the  centre  third  of  the. 
cross-section.  But  the  weight  of  the  dam  itself  must,  neverthe- 
less, be  borne  by  the  foundations,  so  that  the  condition  that  the 
pressure  in  the  masonry  or  on  the  foundations  must  never 

1  As  with  the  Assuan  dam,  the  foundations  of  the  New  Croton  dam 
had  to  be  carried  down  a  considerable  depth — over  40  feet — below  the 
foundation  level  shown  on  the  design. 


IRRIGATION. 


exceed  safe  limits,  must  still  be  complied  with.  The  following 
statement  gives  details  about  four  remarkable  curved  dams, 
three  of  which  are  in  California  : — 


Name  of  Dam. 

Country. 

Maxi- 
mum 
Height. 

Radius 
of  Cur- 
vature. 

Length 
of  Dam 
at  Crest. 

Top 

Width. 

Bottom 
Width. 

Feet. 

Feet. 

Feet. 

Feet. 

Feet. 

Zola     . 

France    . 

123 

158 

205 

19 

42 

See  Fig.  2  1 

Sweetwater  . 

California 

QO 

222 

380 

12 

46 

Bear  Valley 

M 

64 

300 

450 

3-3 

2O 

See  Fig.  22 

Upper  Otay 

M 

75 

359 

350 

4 

14 

Figures  21  and  22  give  the  cross-sections  of  the  Zola  and 
Bear  Valley  dams. 

Reservoirs  that  are  formed  by  solid  dams  holding  up  water 
to  considerable  heights  are  doomed  to  extinction  by  silt  deposit, 
sooner  or  later  according  as  the  proportion  of  silt,  that  is  carried 
in  suspension  by  the  streams  that  fill  them,  is  great  or  small. 
The  small  scouring  sluices,  with  which  some  of  such  dams  are 
provided,  are  efficient  in  removing  the  deposit  of  silt  only  in  cases 
where  the  reservoir  is  very  narrow  and  has  a  very  steep  sloping 
bed.  India,  Algeria  and  Spain  can  furnish  instances  of  reservoirs 
that  have  become  extinct  by  the  silting  up  of  their  basins.  In 
Spain,  the  Val  de  Innerno  dam,1  115  feet  high,  has  been  for 
many  years  a  useless  waterfall,  the  reservoir  basin  having  silted 
up  to  the  crest  of  the  dam.  The  reservoir  above  the  dam  of 
Alicante,  in  Spain  also,  silts  up  to  a  depth  of  40  to  50  feet 
against  the  dam  in  four  years.  The  scouring  sluice  is  then 
brought  into  operation,  and  the  deposit  removed  by  the  escaping 
water.  At  least,  this  should  be  done  every  fourth  year ;  but  the 
intervals  between  two  scouring  operations  is  generally  longer. 
In  the  case  of  the  Alicante  dam,  the  sluice  acts  well  and  the 
reservoir  is  kept  clean,  probably  because  the  basin  is  narrow 
and  steep.  As  the  scouring  sluice  of  the  Alicante  dam  is 
typical  of  the  sluices  of  both  Spanish  and  Algerian  dams,  Sir 
i  «  irrigation  du  Midi  de  1'Espagne,"  by  Aymard. 


DAMS   AND   RESERVOIRS. 


93 


William  Willcocks'  description  of  such  a  sluice  will  be  given. 
Figs.  23  and  24  are  referred  to  in  the  following  description  : 
"  The  under-sluice  at  Khamis  (in  Algeria)  is  on  the  Spanish 
principle.  It  is  situated  at  the  bottom  in  the  line  of  the  bed  of 
the  original  stream.  A  Spanish  under-sluice  consists  of  an 
opening  of  from  i  to  3  metres  in  height,  and  from  i  to  2  metres 

ZOLA      DAM  BEAR     VALLEY     DAM 


Scale 


Mf- 


50 


FIG    2! 


in  width  at  the  up-stream  end ;  it  increases  gradually  as  it 
advances  down-stream,  and  it  is  sometimes  as  much  as  4  metres 
wide  and  6  metres  high.  This  opening  is  closed  at  the  up-stream 
end  by  a  wooden  door,  called  a  Spanish  door,  supported  against 
horizontal  timbers  let  into  apertures  in  the  two  sides  at  the 
point  A  in  the  figures.  Just  above  the  under-sluice  is  a 
gallery.  This  gallery  is  about  a  metre  wide  and  2  metres 
high,  and  is  closed  on  the  up-stream  side,  and  open  on  the 


94 


IRRIGATION. 


down-stream  face  to  allow  workmen  to  enter.  It  communi- 
cates with  the  under-sluice  by  an  opening  some  60  centimetres 
in  diameter  just  down-stream  of  the  gate  A  (Fig.  23). 

The  door  is  put  in  position  in  the  under-sluice  from  the  down- 
stream side  when  the  reservoir  is  empty,  and  the  three  horizontal 
timbers  B,  C,  D  (Fig.  24)  are  let  into  slots  in  the  jambs,  and 
the  whole  door  is  well  caulked.  The  water  now  rises  in  the 
reservoir,  and  as  the  deposits  accumulate,  they  bury  the  door 
and  gradually  gain  great  consistency.  It  takes  four  years  for 

SPANISH    UNDERSLUICES 

FOR.     SCOURING 


FIG    23 


FIG     24- 


SLUICE 


orf 

TtfflMrntfW'-. 


the  deposit  to  become  solid,  though  it  is  generally  left  ten  years. 
When  the  reservoir  has  got  fille^  up  with  deposits  to  the  extent 
which  is  considered  a  maximum,  the  workmen  enter  the  under- 
sluice,  bore  with  an  auger  through  the  door  to  be  sure  that  the 
mud  is  solid,  saw  the  timbers  B,  C  and  D,  and  then  escape  into 
the  gallery.  The  door  is  now  free  to  drop,  but  it  is  generally 
held  by  the  solidified  mud.  The  workmen  now  go  to  the  top 
of  the  dam  and  work  a  hole  through  the  deposit  with  a  long 
iron  pole  until  the  water  touches  the  door.  When  this  happens 
the  door  falls,  and  the  mud  follows  it  in  a  tremendous  avalanche. 
The  reservoir  is  soon  emptied,  and  more  or  less  of  the  deposit 


DAMS   AND   RESERVOIRS. 


95 


removed.     A  new  gate  is  then  put  in,  new  horizontals  B,  C,  D 
are  placed  behind  it,  and  the  reservoir  begins  to  fill  again."1 

Recognition  of  the  liability  to  obliteration  by  deposit  of  silt, 
to  which  most  reservoirs  formed  by  solid  dams  are  subject,  led 
to  the  design  of  an  insubmergible  dam  pierced  with  numerous 

BHATGARH    DAM 

SECTION 
THROUGH      UNDER    SLUICES 


Scale  of  'imitini?        1°      T      T 


40         50 


Feet 


under-sluices.  The  first  specimen  of  this  class  of  dam  was  the 
Bhatgarh  dam  in  India  (Fig.  25),  constructed  about  1892. 
This  dam  has  a  maximum  height  of  127  feet.  There  are  two 
overflow  waste  weirs,  one  at  each  end  of  the  dam.  But  there 
are  also  15  under-sluices,  each  8  feet  by  4  feet,  piercing  the 
dam  near  its  centre,  with  their  sills  12  feet  only  above  the  bed 

1  "  Perennial  Irrigation,  etc.,"  Government  of  Egypt  (1894). 


96  IRRIGATION. 

of  the  river,  which  is  103  feet  below  the  crest  of  the  dam.  The 
object  of  these  sluices  is  to  prevent  the  deposit  of  silt  in  the  reser- 
voir by  providing  a  passage  for  the  early  floods  at  a  low  level. 
If  the  flood  water,  heavily  laden  with  silt,  were  to  be  discharged 
over  the  high  level  waste  weirs,  it  would  drop  the  greater  pro- 
portion of  its  silt  on  the  bed  of  the  reservoir  in  its  passage 
through  the  deep  pond  above  the  dam.  In  ordinary  floods 
the  discharge  through  the  under-sluices  is  effected  under  a  head 
averaging  15  feet,  and  the  ponding  up  extends  to  a  distance  of 
3  miles  above  the  dam.  Consequently  a  certain  proportion 
of  silt  will  be  deposited  in  the  reservoir,  even  when  the  under- 
sluices  are  open  to  pass  the  early  floods.  But  as  they  are 
closed  on  July  3ist,  or  earlier,  to  ensure  the  filling  of  the 
reservoir,  there  will  be  a  further  deposit  due  to  the  later  floods 
which  enter  the  reservoir  basin  after  the  low  level  exit  is  closed. 
Still  it  is  a  great  point  gained  that,  at  the  time  when  the  floods 
are  carrying  the  greatest  amount  of  silt,  the  discharge  is 
allowed  to  flow  forward  through  the  reservoir  with  a  com- 
paratively small  heading-up.  The  surface  of  the  backwater, 
when  the  under-sluices  are  open  and  working  under  a  head  of  15 
feet,  is  less  than  one  thirtieth  of  the  area  of  the  reservoir  when 
full ;  and,  therefore,  twenty-nine  thirtieths  of  the  reservoir  bed 
are  out  of  the  reach  of  silt  deposit.  On  the  remaining  thirtieth 
under  water  there  is  also  less  tendency  to  deposit  than  there 
would  be  if  the  discharge  from  the  reservoir  had  to  find  its 
way  over  the  high  level  waste  weirs.  Undoubtedly  the  action 
of  the  under-sluices  will  be  effectual  in  prolonging  the  life  of 
the  reservoir :  the  experience  of  the  last  twenty-five  years 
has  demonstrated  this. 

The  principle  of  allowing  the  silt-laden  waters  of  floods  to 
pass  through  the  reservoir  basin  without  serious  diminution  of 
velocity  has  been  applied  in  a  more  thorough-going  way  to  the 
design  of  the  Assuan  dam  on  the  Nile.  This  dam  (Fig.  26)  is 
remarkable  as  being  the  first  insubmergible  dam  built  without 
any  provision  of  overflow  waste  weirs  to  discharge  excess  water. 


DAMS   AND   RESERVOIRS. 


97 


The  whole  river  discharge  at  all  times  of  the  year  is  passed 
through  sluices  pierced  in  the  body  of  the  dam,  as  may  be  seen 
on  Plate  I.,  which  is  a  reproduction  from  a  photograph  taken  by 
the  author  on  the  day  after  the  inauguration  of  the  dam.  The 
dam  is  also  remarkable  on  other  accounts.  It  is  about  ij  miles 


ASSUAN      DAM 

Scale 

:    10     6      ?  V  V 


1 T  ** 


FIG     26 


long,  and,  as  originally  built,  even  before  the  subsequent  raising 
and  strengthening,  contained  over  a  million  tons  weight  of 
masonry.  Moreover,  the  available  capacity  of  the  reservoir, 
formed  by  it  in  the  trough  of  the  Nile  itself,  is  greater  than 
that  of  any  artificial  basin  in  the  world.  The  gross  capacity 
of  the  Marikanave  reservoir  in  India  is  said  to  be  30,000,000,000 
cubic  feet,  but  this  can  scarcely  be  reckoned  as  available 
I.  H 


98  IRRIGATION. 

capacity,  since  the  reservoir  is  only  expected  to  fill  once  in 
six  years.  A  reservoir  in  Australia  on  the  Upper  Goulbourn 
river  has  been  credited  with  a  capacity  of  60,000,000,000 
cubic  feet.  The  Assuan  reservoir,  with  the  dam  as  originally 
built,  was  said  to  contain  1,065,000,000  cubic  metres — or 
37,611,000,000  cubic  feet.  After  the  raising  of  the  dam  by 
5  metres  (16-4  feet)  and  of  the  surface  level  of  the  reservoir  by 
7  metres  (23  feet)  above  the  level  used  in  the  calculation  which 
gave  a  resulting  capacity  of  1,065,000,000  cubic  metres,  the 
new  capacity  has  become  2,200,000,000  cubic  metres — or,  in 
round  numbers,  80,000,000,000  cubic  feet.  The  greatest  height 
of  the  completed  dam  is  143  feet.  It  has  now  to  support  a 
maximum  head  of  90  feet.  The  cross  section  of  the  dam,  as 
built  in  the  first  instance,  and  with  the  additions  to  it  subse- 
quently made,  is  as  shown  in  Fig.  26. 

The  past  history  of  reservoirs  is  sufficiently  full  of  warnings 
of  the  danger  that  would  be  run  if  a  solid  dam  were  constructed 
to  impound  such  a  river  as  the  Nile.  During  the  flood  months 
of  August  and  September,  and  sometimes  October,  the  Nile 
water  is  heavily  charged  with  matter  in  suspension.  Any 
obstruction  such  as  a  solid  dam,  which  materially  interfered 
with  the  flow  during  those  months,  would  inevitably  induce  a 
heavy  deposit  of  silt,  and  eventually  cause  the  obliteration  ot 
the  reservoir  basin.  The  dam  might  survive,  but  merely  as  a 
picturesque  waterfall  like  the  Spanish  dam  of  Val  de  Infierno. 
To  avoid  this  danger,  the  Assuan  dam  was  designed  to  pass 
the  whole  Nile  flood  through  under-sluices.  Of  these  there  are 
180  in  number,  all  of  them  2  metres  (6J  feet)  wide,  the  40 
upper  sluices  being  3-5  metres  (nj  feet)  high,  and  the  140 
under-sluices  7  metres  (23  feet)  high.  They  are  placed  in 
groups  at  four  different  levels  in  the  dam,  a  convenient  arrange- 
ment for  regulation.  An  extreme  flood  of  14,000  cubic 
metres  (494,500  cubic  feet)  a  second,  which  comes  but 
seldom,  would  be  passed  through  the  under-sluices,  all  being 
open,  with  a  heading  up  of  about  3-5  metres  (uj  feet) 


DAMS   AND   RESERVOIRS.  99 

and  with  a  resulting  velocity  of  about  6J  metres  (2iJ  feet) 
per  second'.  An  ordinary  flood  will  be  passed  with  a  heading 
up  of  2  or  3  metres  (7  to  10  feet)  only.  Thus  the  turbid 
flood  discharge  will  be  scarcely  interfered  with,  and  there  will  be 
no  danger  of  serious  silting.  Under  normal  conditions  of  the 
river  discharge  the  sluices  remain  open  till  the  end  of  October, 
when  the  water  becomes  comparatively  clear.  During  November, 
December  and  January  the  reservoir  is  filled  by  the  gradual 
closure  of  the  sluices,  commencing  first  with  the  lowest  groups. 
During  February  and  March  the  reservoir  is  kept  full ;  and  in 
April,  May  and  June  its  stored  water  is  drawn  upon  to  supple- 
ment the  deficient  discharge  of  the  river.  Before  the  end  of 
July  all  the  stored  water  has  been  discharged,  and  all  the 
sluices  are  open  ready  to  pass  the  rising  flood. 

The  Assuan  dam  had  been  in  action  for  two  years  when 
the  question  of  raising  it  came  up  for  decision.  During 
that  time  the  severe  action  of  the  water,  discharging  through 
the  sluices  with  a  high  velocity,  had  eroded  the  sound 
granite  beyond  the  down-stream  toe  of  the  dam.  To  have 
raised  the  dam  and  to  have  thereby  added  to  the  head 
of  water  would  have  increased  the  severity  of  the  erosive 
action  of  the  sluice  discharge.  As  extensive  protective 
works,  estimated  to  cost  about  a  quarter  of  a  million  pounds 
and  to  take  two  years  to  complete,  were  necessary  to  secure  the 
dam,  as  it  stood,  against  danger  from  erosion  of  its  natural 
granite  talus,  the  decision  as  to  the  raising  was  postponed  till 
this  work  should  be  complete.  The  granite  bed  of  the  river 
below  the  sluices  had  been  originally  left  in  its  natural  rough 
state  with  an  irregular  suriace,  as  may  be  seen  in  the 
accompanying  photograph  :  it  was  found  necessary  to  substi- 
tute an  apron  of  masonry  in  cement  mortar  with  a  smooth 
surface  to  protect  the  rock  from  the  shock  of  the  falling  water 
and  to  support  the  toe  of  the  dan^  The  protective  aprons 
having  successfully  stood  the  test  of  two  whole  seasons,  it  was 
thereupon  decided  to  raise  the  dam. 

H  2 


100  IRRIGATION. 

The  postponement  of  the  consideration  of  the  question  of 
raising  the  Assuan  dam  had  another  advantage.  It  gave 
time  for  the  further  investigations  of  Professor  Pearson's  and 
Mr.  Atcherley's  new  theory  concerning  stresses  in  dams, 
which  will  be  found  stated  shortly  in  an  abstract  of  Mr.  L.  W. 
Atcherley's  Paper,  published  in  Vol.  162  of  the  Proceedings 
Inst.C.E.,  November,  1905. 

In  the  Assuan  dam  there  is  no  waste  weir  or  outlet  sluice ; 
the  under-sluices  take  their  places.  In  the  Bhatgarh  dam  the 
under-sluices  do  only  a  small  part  of  the  work  of  passing  the 
reservoir  discharge,  and  are  in  action  for  a  short  period  only 
during  the  year ;  the  waste  weirs  of  the  crest,  on  either  flank 
of  the  insubmergible  portion  of  the  dam,  provide  for  the 
outflow  from  the  reservoir  for  the  rest  of  the  year.  Sub- 
mergible  dams  have  no  separate  waste  weirs,  being  themselves 
waste  weirs.  But  insubmergible  solid  dams  and  earthen  dams 
must  have  their  waste  weirs,  and  care  must  be  taken  that  the 
discharging  capacity  of  these  weirs  be  ample.  The  neglect  to 
provide  sufficient  waterway  for  surplus  water  to  escape  has 
caused  the  ruin  of  not  a  few  dams.  If  the  waste  weir  is  high, 
it  often  takes  the  form  of  a  submergible  dam,  as  in  the  case  of 
the  overfall  portion  of  the  Croton  dam  (Fig.  14).  Some  weirs 
have  no  crest  shutters,  discharging  capacity  being  obtained  by 
length  of  crest  with  shallow  depth  of  overflow.  But  sometimes 
it  is  more  convenient,  from  want  of  space  or  for  economical 
or  other  reasons,  to  increase  the  depth  of  overflow  rather  than 
the  length  of  weir.  In  the  waste  weirs  of  the  Bhatgarh  dam 
many  of  the  vents  are  fitted  with  the  automatic  gates  invented 
by  Mr.  Reinold.  Fig.  27  shows  the  principle  upon  which  these 
gates  work.  Each  gate  is  suspended  by  chains  connecting  it 
with  a  counter-weight  which  is  free  to  move  up  and  down  in  a 
water-tight  chamber  formed  in  the  thickness  of  the  weir  wall, 
An  inlet  pipe  admits  water  to  the  cistern  when  the  reservoir  is 
at  full  supply  level,  and  an  outlet  pipe  at  the  bottom  allows  it  to 


DAMS  AND  RESERVOIRS. 


101 


escape.  The  discharge  of  the  outlet  pipe  at  its  maximum  is 
less  than  the  maximum  discharge  of  the  inlet  pipe.  It  will  be 
observed  from  the  drawing  that  the  sluice  is  closed  when  the 
gate  is  raised.  The  automatic  action  is  produced  by  water 
finding  its  way  to  the  cistern  and  reducing  the  lifting  power  of 


REINOLD  S     AUTOMATIC 
SLUICE     GATE 

e  of  ?l   I  I   M  I  I -I  ifl   I   I   l*f  Feet 


FIG    27 


Gale    ofe* 


the  counter-weight  through  immersion.  When  the  water  in  the 
reservoir  rises  to  the  level  of  the  inlet  pipe,  the  cistern  gradually 
fills  and  the  counter-weight  is  immersed.  When  the  counter- 
weight has  in  consequence  lost  sufficient  weight,  the  gate  becomes 
the  heavier  and  moves  downwards  below  the  level  of  the  sluice 
sill,  and  continues  to  do  so  as  long  as  the  water  rises  in  the 


102 


IRRIGATION. 


cistern.  When  the  discharge  through  the  opened  sluice  lowers 
the  water  in  the  reservoir  below  inlet  level,  the  cistern  empties 
itself  of  water  by  its  outlet  pipe,  and  the  counter-weight  regains 
the  weight  necessary  to  pull  up  the  gate  and  close  the  sluice. 

Before  leaving  the  subject  of  dams,  it  may  be  useful  to  give 
the  figures  representing  the  actual  maximum  pressures  on  the 
masonry  in  some  existing  dams,  selected  from  among  old  and 
recent  ones. 


Name  of  Dam. 

Maximum  Pressure. 
Tons  per  Square 
Foot. 

Weight  of  Masonry. 
Pounds  per  Cubic  Foot. 

12-8 

i 

V8o 

Gros  Bois,  France      .... 

14*60 
7'27 

160 

v8o 

•JX  3'C 

Marikanave,  India      .... 
Mundaring,  Australia 
Quaker  Bridge,  New  York  . 

*8-oo 
*8-oo 
16-60 
(designed) 

150 

(New  Croton  dam 
substituted) 

*  Pressure  not  to  be  exceeded  in  accordance  with  conditions  laid 
down  for  design. 

Wilson's  "Manual  of  Irrigation  Engineering"  gives  the 
following  values  for  the  limiting  pressures  which  are  ordinarily 
accepted  as  safe  to  allow  : — 


Brick 
Sandstone 
Limestone 
Granite 


770  tons  per  square  foot. 

8'35  »  v 

9-80  „  „ 

lO'OO  ,  „ 


From  six  to  eight  tons  per  square  foot  may  be  taken  as  the 
pressure  generally  considered  permissible  in  important  dams  of 
recent  construction.  Bold  things,  however,  are  done  in 
America,  and  the  New  Croton  dam  may  show  that  engineering 


DAMS  AND   RESERVOIRS. 

practice  in  the  design  of  dams  has  erred  on  the  side  of  caution. 
It  will  be  observed  that  the  pressure  allowed  for  the  Marikanave 
dam  in  India  and  for  the  Mundaring  dam  in  Australia  is  half 
that  allowed  in  the  design  of  the  New  Croton  dam,  New 
York. 


CHAPTER   VI. 

MEANS  OF   DRAWING   ON   THE   SUPPLY. 

THE  supply  of  water,  as  already  pointed  out,  may  be  drawn 
from  wells,  rivers,  natural  or  artificial  reservoirs,  or  tanks. 
When  a  storage  reservoir  forms  a  feature  of  an  irrigation 
system,  the  supply  drawn  from  it  may  either  be  carried  to  the 
distributing  channels  from  which  the  lands  are  irrigated  in  a 
canal  or  canals  taking  off  direct  from  the  reservoir  itself,  or  be 
sent  on  its  way  along  the  natural  channel  of  the  river  to  the 
point  where  the  canal  system  takes  off.  It  is  only  from  the 
smaller  class  of  reservoirs,  which  are  called  tanks  in  India,  that 
the  distributaries  are  fed  direct.  The  low-lying  reservoirs  of 
the  United  States,  which  are  filled  during  the  flood  season  by 
canals  taking  off  from  a  river,  may  be  classified  as  "  tanks  " ; 
they  deliver  their  water  direct  to  the  channels  that  distribute  it 
to  the  fields. 

When  wells  are  the  source  of  supply,  various  mechanical 
means  are  used  to  raise  the  water.  For  small  lifts  the  shadouf 
of  Egypt — the  Idt  or  picottah  of  India — is  commonly  used ;  for 
deep  wells  in  India  the  mote  is  substituted;  for  medium  lifts 
the  Egyptian  sakia  or  Persian  wheel  is  universal.  The  shadouf 
and  sakia  are  also  used  extensively  along  river  margins  for  the 
irrigation  of  small  holdings.  The  province  of  Dongola,  at  one 
time  reputed  to  be  the  richest  province  in  the  Sudan  (a  reputa- 
tion of  no  very  high  order),  is  irrigated  almost  entirely  by  sakias 
along  the  river  edge,  assisted  by  a  very  few  only  on  wells.1  This 
province  will  therefore  furnish  reliable  statistics  of  what  a  sakia 
is  capable  of  doing,  and  it  is  worth  while  to  note  the  figures.  In 
1904  there  were  at  work  in  Dongola  3,892  sakias,  3  pumps 

1  There  has  been  a  certain  development  of  flood  season  irrigation  of  the 
basin  type  of  late  years. 


MEANS  OF   DRAWING  ON   THE  SUPPLY. 

driven  by  engines  of  an  aggregate  of  50  horse-power,  and 
51  shadoufs.  The  50  horse-power  pumping  plant  and  51  shadoufs 
may  be  assumed  to  be  equivalent  to  58  sakias,  bringing  the  total 
number  of  sakias  up  to  3,950.  The  area  of  taxed  land  in  1904 
was  58,057  acres.  The  population  was  130,000  souls,  inclusive 
of  merchants,  tradesmen,  mechanics,  etc.  So  that  there  was 
i  sakia  to  every  15  acres  of  taxed  area,  and  2*24  persons  per 
acre  or  33  per  sakia.  Apparently  the  area  under  cultivation 
had  reached  the  limit  that  the  population  was  capable  of  taking 
in  hand,  as  there  was  at  least  three  times  that  area  of  cultivable 
land  available  in  the  province,  of  which  two-thirds  was  lying 
fallow. 

The  area  of  crop  that  each  of  the  contrivances  named  can 
keep  watered  is  small,  and  naturally  varies  with  the  lift.  A 
single  shadouf  is  only  equal  to  the  irrigation  of  one  or  two  acres 
of  crop ;  a  mote  or  sakia  can  irrigate,  on  the  average,  eight  acres. 

Shadoufs  are  often  worked  in  tiers,  one  above  the  other,  so  as 
to  effect  a  total  lift  of  15  feet  or  more.  The  Persian  wheel  and 
the  mote  can  be  readily  adapted  to  varying  heights  of  lift  by 
altering  the  length  of  the  endless  chain  carrying  the  water 
buckets  or  pots  in  the  one  case,  and  of  the  rope  and  bullock  run 
in  the  other. 

These  primitive  watering  contrivances  of  the  East  are  well 
adapted  to  farms  of  quite  small  areas,  and  to  communities 
wanting  in  mechanical  skill  and  possessed  of  no  appliances  for 
the  handling  of  more  elaborate  machinery. 

It  is  an  idea  that  suggests  itself  to  most  who  give  their  minds 
to  irrigation  problems  that  the  energy  of  the  wind  could  with 
advantage  be  utilised  to  raise  water.  But  the  wind  is  a  more 
capricious  servant  for  irrigation  to  rely  upon  than  rainfall.  In 
Holland  windmills  for  lifting  water  are  becoming  obsolete  :  the 
reliability  of  pumping  stations  worked  by  steam  power  has 
discredited  the  qualifications  of  the  wind.  But  in  the  arid 
west  of  the  United  States  wind  power  is  not  despised,  as  its 
cost  is  about  two-thirds  of  that  of  steam  power.  A  windmill  in 


106  IRRIGATION. 

America  can  be  depended  upon  for  the  irrigation  of  about 
three  acres  ;  but  if  a  tank,  to  act  as  a  reservoir  to  store  water 
at  times  when  irrigation  is  not  being  carried  on,  is  associated 
with  the  windmill  and  its  pump,  from  five  to  fifteen  acres  can 
be  given  irrigation.  This  contrivance  also  is,  therefore,  only 
suited  to  small  holdings,  and  to  irrigation  on  a  very  modest  scale. 

In  the  Fayum  Province  in  Egypt  and  on  the  Genii  river  in 
Southern  Spain  undershot  wheels,  carrying  pots  or  buckets  at 
their  circumference,  are  made  use  of  to  lift  water  on  to  high 
lands  alongside.  An  ordinary  lift  for  such  wheels  is  15  feet. 
The  amount  of  water  lifted  for  each  revolution  of  the  wheel  is 
small,  but  the  delivery  into  the  high  level  trough  is  continuous. 
To  work  the  wheel  a  drop  of  from  2  to  3  feet  is  required. 
Plate  II.  gives  a  view  of  one  of  these  wheels  in  Egypt,  and 
Plate  III.  of  a  similar  wheel  in  Spain. 

For  large  estates  and  irrigation  on  an  extensive  scale  some 
more  efficient  means  of  drawing  on  the  supply  must  be 
employed.  In  Egypt  the  introduction  of  cotton  and  sugarcane 
cultivation  brought  so  much  gain  to  the  farmer  that  he  was 
able  to  afford  a  centrifugal  pump,  worked  by  steam  power,  for 
the  irrigation  of  his  crops.  Sir  William  Willcocks,  in  "  Egyp- 
tian Irrigation  "  (1913),  gives  the  number  of  such  pumps  as 
nearly  7,000.  Twenty-one  years  ago  the  Egyptian  Government 
itself  was  on  the  point  of  adopting  powerful  pumping  stations 
as  the  sole  means  of  drawing  its  water  supply  from  the  river, 
and  had  actually  made  a  commencement  of  putting  that  policy 
into  practice,  when  better  counsels  prevailed.  For,  when 
irrigation  is  on  the  scale  of  the  Government  system  of  Egypt, 
there  is  a  more  effective  and  economical  way  of  getting  the 
river  water  into  the  canals  than  by  pumping  it.  The  method 
consists  in  raising  the  low  water  level  of  the  river  by  wholly  or 
partially  damming  its  summer  channel,  so  that  the  required 
discharge  may  be  forced  to  flow  into  the  canal  or  canals  taking 
off  from  above  the  dam.  By  this  means  the  difference  of  level 
between  the  land  and  water  surfaces  at  the  canal  head  is 


WATER-LIFTING     UNDERSHOT    WHEEL,    SPAIN. 


MEANS  OF  DRAWING  ON   THE  SUPPLY.  107 

diminished.  The  canal,  connecting  the  pool  above  the  river 
dam  and  the  land  to  be  irrigated,  is  given  a  water  surface  slope 
of  a  less  gradient  than  that  of  the  land  surface,  so  that,  after  a 
certain  distance  from  the  canal  head,  land  and  water  surface 
come  to  one  and  the  same  level. 

The  means  employed  for  heading  up  the  summer  level  of  the 
river  at  the  canal  offtake  will  first  be  considered.  Different 
countries  seem  to  have  their  own  peculiar  type  of  work  by 
which  this  heading  up  is  effected.  The  Indian  type  is  the 
"  anicut,"  a  submergible  solid  weir,  over  which  the  flood  flows, 
the  control  of  the  levels  and  currents  being  provided  for  by 
what  are  known  as  under-sluices,  or  scouring  sluices,  on  one  or 
both  flanks  of  the  weir,  and  sometimes  also  in  the  centre.  The 
Egyptian  type  is  the  "barrage,"  of  French  origin,  as  its  name 
betrays.  A  barrage  may  be  described  as  an  insubmergible 
river  regulator,  formed  of  piers  resting  on  a  platform  at  river 
bed  level  and  rising  above  flood  level.  Vertical  grooves  are 
built  into  or  cut  in  the  piers,  and  shutters  slide  up  and  down  in 
them.  By  lifting  or  lowering  the  shutters  the  level  of  the  water 
in  the  pool  above  the  barrage  is  controlled.  In  flood-time  all 
the  shutters  are  lifted  above  the  water  level,  and  the  river  flows 
unchecked  through  the  vents.  For  general  convenience,  arches 
are  turned  between  the  piers,  and  a  roadway  is  thus  provided 
between  the  two  banks  of  the  river. 

In  France  there  are  several  types  of  river  regulators  of 
ingenious,  and  sometimes  elaborate,  designs.  The  early  Poiree 
dams  were  of  the  needle  kind  with  iron  trestles  as  supports  to 
take  the  pressure  of  the  water  when  the  needles  were  in  place. 
The  Boule  shutters  later  on  were  substituted  for  the  needles, 
the  Poiree  frames  being  retained.  The  Boule  shutters  are 
merely  sluice  gates,  lying  one  above  the  other  in  tiers  vertically 
and  side  by  side  in  rows  horizontally,  fitted  each  one  with  a 
bent  iron  strap  whereby  to  get  hold  of  and  raise  it.  Another 
form  of  closure  is  the  Camere  curtain,1  which  consists  of  narrow 
1  "  The  Improvement  of  Rivers,''  by  Thomas  and  Watt. 


108  IRRIGATION. 

horizontal  strips  of  wood  hinged  together  and  capable  of  being 
rolled  up  by  a  chain  which  passes  round  them,  each  curtain 
reaching  from  the  surface  of  the  water  to  the  sill,  which  is  near 
river  bed  level.  The  curtains  are  supported  by  frames,  which 
either  lie  flat  on  the  floor  during  flood,  or  are  lifted  up  clear  of 
the  water  by  overhead  machines,  so  that  the  river  passes  freely 
without  obstruction  of  any  kind.  These  systems,  however, 
suffer  from  the  usual  delicacy  that  attends  complication  of 
structure,  and,  moreover,  are  ill  adapted  to  rivers  in  which  there 
is  floating  debris.  To  obtain  a  tight  closure  when  any  debris 
has  clung  to  the  frames  is  an  impossibility  with  the  Camere 
curtains  and  a  difficulty  with  the  Boule  shutters. 

The  "  Chamoine "  system,  of  French  origin,  has  been 
imported  into  America,  and  good  examples  of  this  form  of 
regulation  are  to  be  found  on  the  Ohio  and  on  other  rivers  in 
the  States.  The  "  Chamoine  "  apparatus  consists  essentially  of 
three  parts,  viz.,  the  shutter  itself,  the  pivoted  frame  on  which 
the  shutter  rides,  and  the  strut.  The  sill  is  formed  of  a  narrow 
ridge  on  the  floor.  The  bottom  of  the  shutter,  when  erect, 
bears  against  the  up-stream  edge  of  the  sill.  The  frame,  or 
"  horse,"  upon  which  the  shutter  rides,  moves  about  its  pivots 
on  the  floor  immediately  down  stream  of  the  sill.  The  shutter 
is  hinged  near  its  middle  to  the  outer  end  of  the  "  horse  "  about 
which  it  revolves,  and  is  free  to  assume  any  position  between  a 
horizontal  and  a  vertical  one.  The  strut  supports  the  shutter 
and  its  "horse"  when  they  are  raised  and  in  the  closed 
position.  The  lower  end  of  the  strut  rests  against  a  casting  on 
the  floor.  When  this  is  moved  from  the  strut  end,  the  shutter 
falls  under  the  pressure  of  the  water,  turning  about  its  hinge 
along  the  upper  end  of  the  "  horse  "  until  it  lies  flat  behind  the 
sill  with  "  horse  "  and  strut  beneath  it. 

In  America  irrigation  on  a  large  scale  is  of  comparatively 
recent  growth.  Practical  experience  with  old  and  new  ideas  in 
the  design  of  irrigation  works,  and  the  lessons  of  experience  in  a 
country  quick  to  learn,  will  doubtless,  in  due  time,  result  in  the 


DAM    ON    THE    RIVER    GENIL,    SPAIN. 


MEANS  OF   DRAWING  ON   THE   SUPPLY.  ICQ 

evolution  of  a  form  of  river  regulator  which  will  be  recognised 
as  the  American  type.  "  Rock-fill  "  and  "  crib  "  weirs  can  only  be 
considered  as  works  of  a  temporary  nature,  destined  to  be 
replaced  by  more  permanent  structures  when  and  where  the 
interests  affected  are  important  enough  to  justify  and  to  bear 
the  increased  cost  of  construction. 

Perhaps  the  best  known  irrigation  system  in  Spain  is  that 
which  serves  the  fertile  plain  of  Granada,  stretching  away  from 
the  foot  of  the  hill  on  which  the  Alhambra  stands.  Here, 
round  about  the  last  foothold  of  the  Moors  in  Spain,  are  to  be 
found  swift-flowing  canals  meandering  along  the  steep  hill- 
sides and  through  intercepting  rocks  down  to  the  green  plains 
beyond  the  town  of  Granada.  The  water  is  derived  from  the 
river  Genii  and  its  tributary  the  Darro,  which  joins  it  at 
Granada.  The  head  works  of  the  canal  system  are  primitive 
in  the  extreme,  and  are  probably  as  they  were  in  the  time  of 
the  Moors.  Plate  IV.  shows  the  regulating  dam  across  the  river 
Genii  below  the  head  of  the  principal  canal.  It  is  constructed 
of  weighted  trestles  of  the  form  shown  in  Plate  V.,  which  is  the 
photograph  of  a  spur  made  at  a  spot  a  short  distance  above  the 
site  of  the  dam.  But  the  dam,  though  primitive  and  in  need 
of  restoration  after  every  severe  flood,  is  efficient,  if  it  is  to  be 
judged  by  the  results  that  are  visible  from  the  Alhambra 
gardens. 

The  selection  of  a  site  for  the  river  work  which  is  to  hold  up 
the  water  will  depend  upon  many  things.  The  work  must 
naturally  be  at  such  a  point  on  the  river  that  the  canal  which 
takes  off  from  above  it  shall  deliver  its  water  at  country  surface 
at  the  upper  limit  of  the  land  to  be  irrigated  "  free-flow,"  that 
is,  by  gravitation  or  simple  flow  without  the  necessity  of  any 
lift.  The  distance  from  the  first  point  of  irrigation  should,  for 
the  sake  of  economy,  be  as  short  as  possible  consistently  with 
the  fulfilment  of  the  condition  concerning  the  delivery  of  water 
at  country  surface.  But  it  is  not  always  possible  to  secure  the 
minimum.  The  material  of  the  river  bed,  its -cross  section  the 


IIO  IRRIGATION. 

direction  of  the  channel  above  and  below,  the  nature  of  the 
river  banks,  and  much  else,  will  have  to  be  taken  into  considera- 
tion in  the  selection  of  the  best  site.  In  the  case,  however,  of 
a  river  work  intended  to  head  up  water  for  the  canals  of  a 
deltaic  system,  the  selection  of  a  site  is  restricted  to  compara- 
tively narrow  limits,  as  the  work  must  of  necessity  be  placed  at 
the  head  of  the  delta  where  the  river  throws  off  or  divides  into 
branches. 

The  height  to  which  the  summer  level  in  the  river  is  to  be 
headed  up  must  be  first  decided.  The  greater  the  heading  up, 
the  shorter  will  be  the  length  of  canal  along  which  the  water 
must  flow  to  come  to  ground  level.  The  usual  head  for  a  river 
regulator  is  from  10  feet  to  13  feet.  In  Chapter  1 1.,  a  figure  (No.  5 
was  given  showing  the  principle  of  grading  a  canal  fed  by  a 
river  in  flood,  so  that,  after  the  necessary  length  of  flow,  the 
water  should  spread  itself  over  the  land.  In  flood  the  natural 
levels  of  the  river,  under  the  conditions  assumed  in  the  figure, 
are  only  a  few  feet  below  country  level,  so  that,  after  a 
comparatively  short  run,  the  water  in  the  canal  comes  to 
country  level.  But  in  summer  the  levels  of  the  river  are  so 
low  that,  if  a  canal  takes  off  from  it  at  its  natural  level,  it  will 
have  to  flow  a  long  distance  before  its  water  comes  to  land 
surface.  So  it  is  better  to  raise  the  river  level  artificially,  and 
reduce  this  unprofitable  length  of  canal.  Supposing,  for 
example,  that  the  country  level  is  10  units  above  summer  water 
level,  and  that  it  has  a  slope  in  the  direction  that  the  canal 
will  take  of  i  in  10,000  units.  If,  in  such  a  case,  the  canal  is 
designed  to  flow  with  a  water  surface  of  i  in  20,000,  then  the 
summer  water  will  come  to  the  land  surface  after  a  run  of 
200,000  units,  or — adopting,  for  convenience'  sake,  metres  as 
the  unit — 200  kilometres  (Fig.  28).  Now,  supposing  that 
the  summer  level  of  the  river  is  artificially  raised  4  units,  or 
metres,  the  canal  water  comes  to  land  surface  at  a  point 
120,000  units,  or  120  kilometres,  from  the  head  instead  of  200 
kilometres.  This  arrangement  results  in  a  great  saving  of 


RIVER    SPUR,    SPAIN. 


MEANS   OF   DRAWING   ON   THE   SUPPLY. 


Ill 


expenditure  on  the  earthwork  of  the  canal  excavation,  balanced 
to  some  extent  by  the  cost  of  the  head  works  in  the  river. 
But,  neglecting  the  question  of  economy,  this  advantage  has 
been  gained,  namely,  that  the  country  between  kilometres  120 
and  200,  or  on  a  length  of  80  kilometres,  is  now  commanded 
by  the  canal  and  can  be  given  free-flow  irrigation.  The  diagram 
(Fig.  28)  shows  the  country  level  and  the  summer  water  levels 
as  they  would  be  with  and  without  artificial  heading  up  of  the 
river. 

It  has  been  stated  above  that  10  feet  to  13  feet  is  the  usual 
amount  of  heading  up  that  river  regulators  are  called  upon  to 
effect.  But  there  is  a  well-known  work  in  Egypt — the  Delta 
barrage — which,  with  the  help  of  a  recently  built  subsidiary 
weir  below  either  section  of  it,  now  holds  up  20  feet,  each 


FIG 


work  undertaking  half  the  head.  If  a  project  contemplated  so 
considerable  a  heading  up  as  this,  the  division  of  the  head 
between  two  separate  works  would  probably  be  considered 
advisable,  and  the  Delta  barrage  principle  be  imitated.  For  a 
single  work  it  has  hitherto  been  considered  wise  to  limit  the 
head  to  13  feet  when  the  work  has  to  be  founded  on  the 
ordinary  sandy  bed  of  a  river.  But  the  "Grand  Anicut "  of 
Madras,  which  is  said  to  have  been  constructed  sixteen  hundred 
years  ago,  and  which  was  until  quite  recently  in  effective  use, 
had  its  crest  15  to  18  feet  above  the  bed  of  the  river,  though 
composed  only  of  rough  stone  set  in  clay  without  mortar  of 
any  kind.  The  Kistna  weir,  built  in  1855,  has  its  crest  16 
feet  above  summer  level  and  25  feet  above  the  deepest  part  of 
the  original  bed. 

In  deciding  upon  the  design  of  the  river  regulator,  the  effect 


112  IRRIGATION. 

that  the  obstruction,  which  it  creates  in  the  river  channel,  will 
have  on  the  flood  discharge  must  be  carefully  considered.  If 
the  backing  up  of  the  water,  or  "afflux,"  should  be  consider- 
able, there  may  be  danger  of  causing  inundations  in  consequence 
of  the  higher  flood  levels  produced,  and  danger,  perhaps,  of 
the  flanks  of  the  river  work  being  turned  by  the  flood  water. 
The  solid  immovable  part  of  the  regulator,  which  remains 
through  the  flood,  must  not  therefore  obstruct  so  great  an  area 
of  the  flood  waterway  as  to  affect  the  high  water  levels 
inconveniently.  In  the  case  of  the  Egyptian  barrages  and 
regulators  of  the  French  type,  the  obstruction  offered  to  the 
flow  is  slight,  as  the  shutters  which  effect  the  heading  up  at 
low  supply  are  removed  clear  of  the  water  during  flood.  The 
design  of  the  French  types  provides  for  the  removal  also  of 
the  supports  against  which  the  shutters  bear. 

In  India,  where  the  regulator  takes  the  form  of  a  solid  weir 
called  an  anicut/it  has  been  found,  as  the  result  of  experience, 
that  the  afflux  is  not  the  only  effect  of  a  solid  obstruction  that 
makes  it  desirable  to  limit  the  height  of  the  weir.  In  the  case 
of  anicuts  of  ordinary  height,  many  examples  of  which  exist 
in  India,  the  afflux  in  flood  is  not  sufficient  to  be  a  serious 
objection.  But  in  several  cases  it  has  been  found  that  the 
obstruction  of  the  flood  waterway  causes  irregular  silting  up 
of  the  river  bed  above  the  anicut,  and  that  the  summer  channels 
are  inconveniently  affected  thereby.  Sometimes  on  this  account, 
and  sometimes  from  other  causes,  a  sufficient  discharge  could 
not  be  forced  into  the  canals  at  low  supply ;  consequently,  in 
such  cases,  it  has  been  found  necessary  to  add  crest  shutters 
along  the  whole  length  of  the  anicut  to  raise  the  summer  level 
still  higher,  so  that  the  river  water  may  flow  into  the  canals. 
These  shutters  are  so  designed  that  they  may  be  laid  flat 
in  the  flood,  and  not  cause  any  additional  obstruction  to  the 

1  A  critic  objects  to  "  the  term  '  anicut'  as  purely  a  Madras  word,  which 
is  neither  used,  nor  even  generally  understood,  in  other  parts  of  India."  But 
the  Sone  weir  in  Bengal  was  known  as  the  "  Dehri  anicut,"  and  the  Sone 
engineers  were  familiar  with  the  term. 


MEANS  OF  DRAWING  ON  THE  SUPPLY.  If  3 

flow.  Profiting  by  the  lessons  taught  by  experience,  the  irriga- 
tion engineers  of  India  have  recently  shown  a  preference  for 
low  weirs  with  crest  shutters,  and  the  later  designs  take  this 
form.  The  crest  shutters  are  usually  from  2  to  3  feet  high,  but 
in  some  cases  are  6  feet  high. 

An  anicut  is  made  up  of  the  weir  proper  and  of  one,  two,  or 
more  groups  of  "  under-sluices."  These  "  under-sluices  "  are 
regulating  openings  in  the  weir,  divided  up  into  bays,  fitted 
with  some  form  of  regulating  shutters.  They  are  sometimes 
called  "  scouring  sluices,"  a  term  to  be  preferred  to  the  more 
commonly  used  "  under-sluices."  The  floor  of  the  sluices  is 
at  or  about  the  level  of  the  bed  of  the  deepest  channel  of  the 
river  at  the  site  of  the  weir.  It  was  expected  by  the  original 
designers  that  the  control  of  the  flood  currents,  which  the  power 
of  opening  and  closing  the  sluices  would  give,  would  make  it 
possible  to  maintain  the  deep  channels  of  the  river  along  such 
lines  as  might  be  desired,  and  that  silting  up  of  the  river  bed 
above  the  weir  would  be  prevented.  But  the  influence  of  the 
under-sluices  has  been  disappointing,  and  the  expectations  have 
been  only  partially  realised.  In  the  case  of  the  Sone  anicut 
in  India,  under-sluices  were  provided  on  each  flank  of  the  weir, 
below  the  offtake  of  the  canals  on  the  right  and  left  banks  of 
the  river,  in  order  to  create  a  draw  past  the  canal  heads.  There 
were  also  added  (but  not  without  misgivings)  under-sluices  in 
the  centre  of  the  weir,  which  were  expected  to  prevent  silting 
above  the  weir  and  to  maintain  a  navigable  channel  across  the 
rurer.  They  have  done  neither  ;  and  so,  as  they  were  very 
troublesome  to  manipulate,  they  have  now>  after  being  in  use 
for  thirty  years,  been  permanently  built  up. 

The  difficulty  caused  by  the  irregular  silting  of  the  river  bed 
above  an  anicut  may  be  lessened  in  some  cases  by  a  judicious 
selection  of  the  anicut  site.  A  straight  reach  of  the  river, 
where  the  cross-section  is  constant  and  the  velocity  of  flow 
uniform,  offers  favourable  conditions.  A  site  where  the  river  is 
abnormally  wide,  though  it  may  afford  facilities  of  construction, 
is  not  favourable  to  the  prevention  of  irregular  silt  deposit.  It 

I.  I 


114  IRRIGATION. 

would  be  better,  if  such  conditions  offer,  to  select  a  site  where 
the  general  width  of  the  river  is  rather  less  than  the  normal 
as  the  one  most  likely  to  be  free  from  the  silt  trouble.  The 
increase  of  velocity  over  the  weir  itself,  due  to  less  length, 
might  necessitate  somewhat  heavier  stone  in  the  talus ;  but,  if 
so,  the  expense  would  be  balanced  by  the  economy  resulting 
from  the  shorter  length  of  weir.  But,  though  the  average  rate 
of  flow  would  be  greater  in  the  shorter  weir,  the  maximum 
velocity  might  even  be  less,  as  the  flow  over  the  longer  weir 
would  not  be  so  uniform  in  consequence  of  the  silt  deposit 
above  it  interfering  with  the  even  flow.  It  is  irregular  silting 
that  is  objectionable  as  giving  rise  to  currents  which  are  not  at 
right  angles  to  the  line  of  the  weir  and  which  may  besides  have 
locally  a  high  velocity.  Uniform  silting  against  the  weir  along 
its  up-stream  face  and  over  the  adjacent  river  bed  is  beneficial 
as  adding  to  the  strength  and  impermeability  of  the  work. 

In  all  cases  in  which  the  bed  of  the  river  is  sandy,  the  weir 
should  be  built  at  right  angles  to  the  direction  of  the  stream. 
There  are  exceptional  cases,  where  the  river  bed  is  rocky  or 
strewn  with  boulders,  and  the  river  velocity  is  high,  in  which  it 
may  be  advantageous  to  adopt  an  alignment  inclined  to  the 
stream.  Figs.  29,  30,  33,  34,  and  35  give  cross-sections  of  those 
weirs  of  the  Indian  type  which  have  been  selected  as  examples 
of  the  different  varieties  of  design  adopted.  The  weir  below 
the  Delta  barrage  is  given  as  the  Egyptian  variety,  the  design 
being  based  on  that  of  the  Sone  weir,  but  having  its  own 
points  of  originality.  The  different  varieties  are  classified  as 
follows : — 

(1)  Weir  with  vertical  drop  on  to  impervious  floor :  to  this 
class  belong  the  Narora,  Burra,  and  Baiturnee  weirs ; 

(2)  Weir  without  drop,  but  with  impervious  floor  sloping 
downwards    from    the    weir  crest  :    to  this  class  belong  the 
Chenab  and  Godavery  weirs ; 

(3)  Weir  without  impervious  floor  or  drop,  but  with  slope  of 
stone  with  open  joints  inclined  downwards  from  weir  crest :  to 


MEANS  OF  DRAWING  ON   THE   SUPPLY. 

this  class  belong  the  Sone,  Mahanadi,  Brahmini,  Kistna,  and 

Okla  weirs,  and  also  the  Egyptian  weir. 

The  Narora  weir  has  been  selected  as  an  illustration  of  the 
first  class,  for  it  has  a  record  which  is  instructive.  It  was 
originally  built  as  in  Fig.  29.  A  weir  of  this  description,  in 
common  with  weirs  of  the  other  classes,  has  to  guard  against 
the  danger  of  the  overflow  scouring  holes  in  the  river  bed  along 
the  down-stream  toe  of  the  talus,  and  cutting  backwards  till  the 
main  body  of  the  work  is  reached  and  undermined.  The  deep 

NARORA      WEIR 


A3     ORIGINALLY     CONSTRUCTED 


no 


AS     STRENGTHENED       ,  FIG    30 


Feet 


curtain  wall  along  the  down-stream  edge  of  the  floor  of  the 
Narora  weir  was  designed  to  meet  this  danger.  But  a  curtain 
wall  in  such  a  position  does  not  give  absolute  security ;  it  is,  at 
best,  but  the  second  line  of  defence  against  the  scour  which  may 
threaten  the  stability  of  the  work.  The  talus  of  heavy  stones 
is  the  first  line  of  defence,  and  whenever  any  of  this  is  displaced 
in  consequence  of  the  scouring  out  of  holes  by  eddies,  or  through 
the  sweeping  away  of  the  stones  by  the  high  velocity  current, 
the  holes  must  be  filled  up  and  the  slope  re-made  to  its 
original  height,  with  still  heavier  stones  than  before  if  found 
necessary* 

I  2 


I  16  IRRIGATION. 

Another  danger  to  which  weirs  in  general  are  subject  is 
leakage  under  the  weir  main  wall  or  floor,  known  as  "piping." 
When  subjected  to  a  head  of  water  there  is  always,  in  the  case 
of  weirs  built  in  sand,  movement  of  water  under  the  weir  from 
up  stream  to  down  stream.  But  if  the  resistance  encountered  is 
sufficiently  great,  the  rate  of  flow  is  so  low  that  the  foundation 
bed  of  the  weir  is  not  disturbed.  Should,  however,  a  run  be 
created  in  which  the  velocity  of  flow  is  high  enough  to  carry  along 
grains  of  sand,  by  degrees  the  leak  will  increase  until  it  undermines 
the  weir  and  causes  its  failure.  The  failures  of  the  under-sluices 
of  the  Mahanadi  weir  in  1886,  and  of  the  Chenab  weir  in 
1895,  were  ascribed  to  this  cause;  and  the  Delta  barrage  in 
Egypt  suffered  from  the  same  defect  in  1867.  This  form  of 
danger  is  aggravated  by  the  scouring  action  of  parallel  currents 
whenever  they  establish  themselves  along  the  front  of  the  weir 
from  faulty  alignment  or  other  cause.  Such  action  must  be 
guarded  against  by  constructing  long  spurs  at  right  angles  to 
the  weir  to  guide  the  flow  into  the  right  direction. 

But,  besides  these  dangers  common  to  most  weirs,  the  form 
of  which  the  Narora  weir  is  an  example  has  two  other  forces 
to  resist.  The  one  is  the  force  of  the  water  falling  on  to  the 
floor  over  the  weir  wall ;  the  other  is  the  force  exerted  on  the 
under-side  of  the  floor,  tending  to  lift  it,  due  to  the  pressure 
developed  when  the  weir  is  holding  up  a  head  of  water.  The 
first  is  easily  met  by  giving  the  floor  sufficient  thickness  and 
covering  it  with  ashlar  blocks.1  If  the  ashlar  is  properly 
bedded,  there  need  be  no  fear  of  failure  in  the  case  of  a  weir  of 
slight  fall,  such  as  anicuts  have,  in  consequence  of  the  action  of 
the  water  falling  on  its  floor  surface.  But  the  other  form  of  force, 
which  is  applied  to  the  under-side  of  the  floor,  is  not  so  easily 
disposed  of,  and  its  mode  of  action  must  be  carefully  studied. 
The  Narora  weir  is  a  useful  example  for  consideration,  for  it 
failed  in  1898,  and  its  failure  has  been  the  cause  of  much 
fruitful  discussion. 

4  but  see  remarks  on  p.  141  concerning  ashlar  coverings. 


MEANS  OF   DRAWING   ON   THE  SUPPLY.  I  I/ 

The  upward  pressure,  due  to  the  head  on  the  weir,  decreases 
in  its  transmission  through  sand  in  proportion  to  the  distance 
travelled.  It  is  a  maximum  at  the  starting-point,  and  practically 
nothing  at  the  point  where  it  finds  an  exit  below  the  weir,  pro- 
vided that  the  floor  is  long  enough  to  reduce  the  issue  of 
percolation  water  along  the  line  of  exit  to  a  mere  trickle.  The 
pressure  at  any  point  can,  therefore,  be  found  by  drawing  a  right- 
angled  triangle  with  its  base  representing  the  path  which  the 
water  has  to  travel  between  the  starting-point  and  the  point  of 
exit,  and  with  the  perpendicular  to  the  base  representing  the 
head  of  water.  The  "  hydraulic  gradient  "  is  then  represented 
by  the  hypothenuse  of  the  triangle,  and  the  pressure  at  any 
point  along  the  path  of  the  water  by  the  line  drawn  perpen- 
dicularly from  the  corresponding  point  of  the  base  to  the 
hypothenuse.  If,  for  example,  the  path  of  travel  is  100  feet 
and  the  head  12  feet,  then  at  25  feet  distance  from  the  starting- 
point  the  pressure  will  be  that  due  to  a  head  of  9  feet,  at 
50  feet  distance  to  a  head  of  6  feet,  and  so  on.  Thus  it  will  be 
clear  that  the  shorter  the  path  the  steeper  will  be  the  hydraulic 
gradient,  and,  therefore,  the  higher  the  rate  of  flow.  The  path 
of  travel  is  assumed  to  follow  the  face  of  the  masonry,  whether 
it  is  horizontal  or  vertical.  Assuming  that  the  material  offering 
resistance  to  the  flow  is  uniform  throughout  the  path  of  travel, 
the  line  representing  the  hydraulic  gradient  will  be  a  straight 
line. 

Only  a  few  days  before  the  floor  of  the  Narora  weir  was 
lifted  two  pipes  had  been  fixed  in  the  floor  in  communication 
with  the  under-side  at  the  points  shown  in  the  accompanying 
sketch  (Fig.  31),  with  the  object  of  ascertaining  the  pressure  by 
direct  observation,  as  some  doubts  were  entertained  concerning 
the  stability  of  the  work.  The  insertion  of  the  pipes  had  nothing 
to  do  with  the  accident,  as  that  occurred  in  a  quite  different 
part  of  the  weir.  At  the  time  of  the  experiment  the  head  on 
the  weir  was  about  12  feet.  The  height  to  which  water  rose  in 
the  pipes  showed  that,  at  a  point  about  13  feet  from  the 


118  IRRIGATION. 

up-stream  face  of  the  weir  wall,  the  upward  pressure  was  that 
due  to  a  head  of  n  feet  of  water;  and  that  34  feet  from  the 
same  face  the  pressure  was  that  due  to  a  head  of  about  10  feet, 
Such  being  the  case,  and  the  floor  being  only  5  feet  thick, 
matters  would  be  critical  when  the  river  bed  below  should 
become  dry.  Mr.  Buckley,  relying  on  an  official  report,  thus 
describes  the  giving  way  of  the  floor :  "  In  March,  1898,  some 
350  feet  of  the  floor  of  this  weir  was  *  blown  up  '  by  the  water 

NARORA     WEIR 

SHOWING    OBSERVATION     PIPES 


W.L.    9*4 


FIG     31 


pressure  below  it  ...  At  the  time  of  the  accident  a  strong 
spring  burst  through  the  floor  at  the  toe  of  the  crest  wall,  and, 
passing  under  the  stone  flooring,  lifted  it  bodily  over  a  length 
of  340  feet  to  a  maximum  height  of  2*23  feet.  The  weir  wall 
settled,  in  a  length  of  120  feet,  about  3  inches,  and  the  flooring 
showed  vertical  cracks.  The  grouted  pitching  below  the  floor 
was  *  blown  up.'  Up  stream  of  the  part  of  the  weir  which  was 
damaged  the  apron  had  disappeared,  and  the  wall  was  exposed 
to  a  depth  of  8  or  9  feet.  Borings  through  the  floor  revealed 
cavities  below  it  extending  to  about  50  feet  on  each  side  of 
the  point  of  fracture."  The  original  puddle  up  stream  of  the 
weir  wall  had,  previously  to  the  accident,  been  scoured  out, 


MEANS  OF   DRAWING   ON    THE  SUPPLY.  119 

and  had  been  replaced  by  block  kankar.  Consequently  the 
starting-point  of  underneath  flow  was  against  the  weir  wall 
itself. 

On  the  assumption  that  the  floor  of  the  weir  was  blown  up, 
it  would  appear  that  the  upward  pressure  was  too  strong 
for  the  floor,  or  the  floor  was  too  weak  to  resist  the 
upward  pressure.  There  were  two  possible  remedies  :  either 
to  make  the  floor  strong  enough  by  building  on  the  top 
of  it,  or  to  reduce  the  pressure  under  the  floor.  The  latter 
was  the  remedy  adopted.  The  starting-point  of  underneath 
flow  was  removed  80  feet  up  stream,  and  thereby  not 
only  was  the  pressure  under  the  floor  reduced,  but  the 
hydraulic  gradient  was  considerably  flattened  out — conditions 
favourable  to  stability  and  prevention  of  "  piping."  This 
result  was  obtained  by  adding  up  stream  of  the  weir  wall  an 
apron  of  puddled  clay  2j  feet  thick,  with  its  surface  and  up- 
stream end  protected  from  scour  by  a  layer  of  pitching  and  a 
bounding  wall  of  kunkur  masonry,  as  shown  in  Fig.  30.  The 
up-stream  face  of  the  weir  was  secured  against  the  danger 
arising  from  parallel  currents  by  the  construction  of  additional 
groynes  to  act  as  guiding  spurs.  A  dwarf  wall,  3  feet  high, 
was  added  along  the  down-stream  edge  of  the  floor  to  form 
a  cushion  of  water  below  the  drop  of  the  weir  wall.  This 
cushion  would  also  have  the  effect,  when  the  river  bed  below 
the  weir  was  dry,  of  adding  weight  to  the  floor,  and  of 
counterbalancing  3  feet  of  the  upward  pressure. 

The  condition  of  things  at  the  time  of  the  accident,  as  well 
as  since  the  additions,  is  shown  in  Fig.  32.  It  will  be  seen 
from  the  diagram  that  the  upward  pressure  on  the  floor  below 
the  drop  has  been  reduced  from  loj  to  6f,  that  is,  to  a  pressure 
due  to  6|  feet  head  of  water,  of  which  3  feet  is  balanced  by  the 
water  cushion  on  the  floor.  So  that  there  remains  a  head  of  only 
3|  feet  to  be  resisted  by  the  effective  weight  of  the  masonry  floor 
of  5  feet  thickness  (i.e.,  gross  weight  of  floor  less  the  weight  of 
water  displaced). 


120 


IRRIGATION. 


Another  advantage  of  extending  the  impervious  part  of  the 
work  on  the  up-stream  side  of  the  point  where  the  heading  up  is 
effected  is,  that  the  extension  can  be  economically  made  of  clay 
puddle,  as  the  upward  pressure  is  more  than  counterbalanced 
by  the  weight  of  water  above.  Clay  puddle,  with  its  surface 
protected  from  scour,  is  as  good  as,  or  better  than,  masonry 
in  such  a  situation,  provided  that  the  junction  of  the  puddle 
and  masonry  is  made  absolutely  secure  against  a  leak.  In 
fact,  if  it  were  not  for  the  necessity  of  resisting  the  pound- 
ing and  scouring  action  of  the  water  down  stream  of  the 

DIAGRAM 

TO  SHOW   PRESSURES    ON    FLOOR    OF      NARORA     WEIR 


5 — 


PUDDLE 


•84"  •  •  •<*•• 
xWELLSx     FLOOR        * 

:fcil  H  1 


WELLS 


GROUTED 
PITCHING 


KAS    ORIGINALLY    CONSTRUCTED 
AS         .STRENGTHENED 


point  of  heading  up,  the  impervious  part  of  the  work 
might  all  be  up  stream.  The  full  lines  of  the  diagram  of 
the  hydraulic  gradient  and  pressures  (Fig.  32)  have  been  drawn 
on  the  assumption  that  the  water  has  to  pass  underneath  the 
deep  curtain  wells;  but  as  the  interstices  between  wells, 
especially  circular  ones,  are  difficult  to  make  water-tight,  the 
path  of  the  water  probably  passes  between  the  wells.  If  the 
depth  of  the  wells  is  excluded  from  the  path,  the  hydraulic 
gradient  will  have  a  shorter  base  and  will  become  steeper,  and 
the  pressure  on  the  grouted  pitching  be  increased,  as  shown  by 


MEANS  OF  DRAWING   ON    THE   SUPPLY.  I2, 

the  dotted  lines.  It  will  be  found  that,  with  this  correction, 
the  upward  pressure  at  the  point  below  the  drop  wall  was  that 
due  to  lof  feet  head  before  the  addition  of  the  up-stream  apron, 
and  is  now  6  feet. 

Although  the  cause  of  the  failure  of  the  weir  may  have  been 
wrongly  ascribed  in  official  reports  to  the  "  blowing  up  "  of  the 
weir  floor,  still,  had  there  been  no  failure,  the  observation  pipes 
had  disclosed  the  critical  condition  of  the  floor  and  demonstrated 
the  necessity  for  the  additions  made. 

There  are  several  theories  regarding  the  manner  in  which 
this  weir  failed,  and  the  local  engineers  decline  to  commit 
themselves  to  a  positive  opinion.  If,  as  seems  to  be  generally 
admitted,  the  grouted  pitching  beyond  the  floor  was  "  blown 
up,"  it  is  difficult  to  understand  how  the  floor  could  have  been 
also  "  blown  up."  The  blowing  up  of  the  pitching  could  not 
have  occurred  after  the  blowing-up  of  the  floor  had  reduced  the 
upward  pressure  on  the  pitching :  nor  is  it  likely  that  the  floor 
could  have  been  lifted  after  the  blowing  up  of  the  pitching  had 
reduced  the  pressure.  An  engineer  of  experience,  who  visited 
the  work  not  long  after  the  accident,  is  of  opinion  that  the 
grouted  rubble  was  first  blown  up,  causing  a  loud  report :  the 
rush  of  water  through  the  hole,  thus  formed,  scoured  out  the 
sand  from  below  the  weir :  the  floor  subsided  into  the  cavity, 
and,  dislocation  of  the  masonry  resulting,  a  strong  spring 
issued  at  the  toe  of  the  crest  wall,  and  the  water  under  pressure, 
finding  its  way  between  the  separated  layers  of  masonry,  lifted 
the  ashlar  covering  of  the  floor.  If  this  is  the  real  sequence  of 
events,  the  moral  is  stated  in  conclusion  No.  4  below. 

A  consideration  of  the  diagrams,  Figs.  31  and  32,  leads  to 
the  following  conclusions  : — 

(i)  That  extension  of  the  impermeable  platform  up  stream  of 
the  drop  wall  decreases  the  upward  pressure  on  the  floor  below 
the  drop  wall  at  the  same  time  that  it  reduces  the  steepness  of 
the  hydraulic  gradient  and,  therefore,  the  rate  of  flow  of  the 
percolation  water ; 


122  IRRIGATION. 

(2)  That    extension    of   the    impermeable    platform    down 
stream  has  the  disadvantage  of  increasing  the  upward  pressure 
on  the  floor  below  the  drop  wall,  though  the  steepness  of  the 
hydraulic  gradient  is  favourably  affected  in  the  same  way  as  by 
an  up-stream  extension ; 

(3)  That  for  these  reasons  a  curtain  wall  is  well  placed   if 
up  stream  of  the  floor,  but  badly  placed  if  down  stream,  except 
as  a  precaution  against  cutting  back  and  undermining  of  the 
floor;  and — 

(4)  That  it  is  a  mistake  to  grout  pitching  on  the  down-stream 
side  of  the  floor,  it  being  assumed  that  the  water-tight  floor 
below  the  drop  wall  is  made  strong  enough  and  wide  enough 
to  withstand  the  impact  of  the  falling  water. 

The  case  of  the  Narora  weir  has  been  examined  at  length, 
as  it  exemplifies  the  principles  on  which  the  designs  of  recent 
constructions  have  been  based.  There  will  be  the  less  to  say 
about  the  other  varieties  of  weirs. 

The  Chenab  weir  (Fig.  33),  which  has  been  selected  as  an 
example  of  class  (2)  (no  drop,  sloping  impervious  floor),  has  a 
similar  history  to  the  Narora  weir.  It  failed  from  "  piping," 
or  leakage  under  the  floor.  As  originally  built,  there  was 
only  a  triangle  of  stone  pitching  with  a  base  of  24  feet 
up  stream  of  the  main  weir  wall.  Since  the  failure  an  apron 
of  surface-protected  clay  puddle  has  been  added  up  stream 
of  the  weir  wall,  as  in  the  case  of  the  Narora  weir.  It 
is  doubtful  whether  the  addition  of  a  line  of  piles  or  wells  to 
the  clay  apron  is  a  proceeding  to  be  recommended.  Certainly, 
if  they  form  deep  water -tight  curtains,  they  are  more  effective 
in  preventing  "piping"  than  a  corresponding  length  of  hori- 
zontal apron  would  be,  as  they  alter  the  direction  of  the  flow 
and  check  the  movement  of  the  sand,  p  But  if  the  intervals 
between  piles  or  wells  are  not  perfectly  filled  and  rendered 
water-tight,  they  do  more  harm  than  good,  as  the  unfilled  intervals 
form  vertical  runs  by  which  deep  springs  from  the  river  bed 


MEANS   OF   DRAWING  ON    THE   SUPPLY. 


123 


find  a  free  passage  upwards  to  the  under-side  of  the  floor.  The 
subject  of  wells  and  piles  will  be  further  discussed  in  the  next 
chapter  when  considering  the  different  methods  of  constructing 
sub-aqueous  foundations. 

The  third  class  of  weirs,  of  which  the  Sone  weir  is  selected 
as  an  example,  has  no  impervious  floor,  but  is  made  of  two 
(sometimes  three)  parallel  walls,  generally  founded  on  wells 
sunk  in  the  river  bed.  The  spaces  between  the  walls  are  filled 
with  rubble  pitching,  with  a  carefully  packed  surface  of  large 

CHENAB     WEIR 


FIG     33 


W.L. 


VOfTCKSTE      COVKRIHO 


m 


.-42- -f-8f- 68 f -42 +-104—  45 

r*  £— -Impermeable 179'  Platform - *      ' 

k...    »«.w.p.«*-.*._-— .--—    TQt-al      Width.     26*'  -_ 


DELTA    BARRAGE     WEIR 

Total   Width      207' 


FIG    34 


stones  on  end.  The  pitching  is  continued  beyond  the  lower 
wall.  The  cross-section  (Fig.  35)  gives  the  design  and  dimen- 
sions of  the  Sone  weir.  In  the  case  of  this  weir,  10  feet  is  the 
total  head.  This  is  equally  divided  between  the  two  walls,  if 
both  are  water-tight. 

The  Okla  weir  is  remarkable  for  being  constructed  on  the 
surface  of  the  river  bed  without  any  foundations  below  that 
level.  There  are  three  walls.  The  maximum  head  on  the  weir 
is  13  feet.  The  main  wall  holds  up  4  feet,  the  middle  wall 
4  feet  3  inches,  and  the  lowest  wall  4  feet  g  inches;  that  is, 
supposing  that  the  river  below  is  dry  and  that  all  the  walls  are 


124 


IRRIGATION 


water-tight.  The  percolation  along  the  river  bed,  under  each 
wall,  keeps  the  interspaces  full  of  water,  and  so  causes  a  division 
of  the  head  between  the  walls. 

The  Sone  weir  was  the  type  which  influenced  the  design  of  the 
Delta  barrage  weir  in  Egypt.  The  cross-section  given  of  the 
latter  (Fig.  34)  is  sufficient  to  show  the  design  without  explana- 
tion. The  manner  of  building  the  Delta  barrage  weir  will  be 
described  in  the  next  chapter.  It  was  important  that  the  weir 
should  be  made  as  water-tight  as  possible  in  order  that  there 

SONE     WEIR 


• 80 *  4  * • 

„ Slot* 


.-« Total -Width-..  125' a" 


CREST      SHUTTERS 


FIG      36 


might  be  no  loss  in  summer  when  the  water  was  standing  level 
with  the  weir  crest.  Mr.  R.  B.  Buckley,  who  is  an  authority  on 
these  matters  and  knows  both  the  Sone  and  Egyptian  weirs,  has 
stated  in  a  discussion  comparing  the  two  weirs  that,  "while  the 
Sone  weir  fulfilled  its  purpose  absolutely,  it  was  not  water- 
tight," and  added,  "  The  subsidiary  weirs  on  the  Nile  were  the 
most  water-tight  weirs  that  had  ever  been  built."1  The  core 
wall,  with  its  up-stream  clay  weighted  with  rubble,  forms  a 
perfectly  water-tight  bar  across  the  river.  The  utility  of  the 
down-stream  clay  is  doubtful,  but,  compressed  as  it  is  by  a  great 
depth  of  rubble,  it  may  help  to  preserve  a  tight  joint  with  the 
1  Proceedings  last.  C.E.,  Vol.  CLVIII.,  Part  IV. 


MEANS  OF   DRAWING   ON   THE  SUPPLY.  125 

river  bed.  At  any  rate,  it  removes  the  point  where  percolation 
can  first  escape  upwards  to  some  distance  from  the  core  wall. 
The  footing  wall  is  also  given  a  water-tight  joint  with  the  bed 
by  means  of  up-stream  clay,  so  that  the  maximum  head  on  the 
core  wall  is  limited  to  the  difference  in  level  between  the  crests 
of  the  two  walls.  The  weir  holds  up  altogether  about  10  feet. 
Probably  it  could  do  more  if  required,  as  it  is  considered  by 
some  to  be  abnormally  strong. 

The  heavy  blocks  of  the  weir  tail  are  intended  to  stop  cutting 
back  towards  the  footing  wall.  Should  any  holes  be  scoured 
out  along  the  down-stream  margin,  the  blocks  would  subside 
into  them  and  check  the  action  sufficiently  to  carry  the  work 
safely  through  the  flood.  Before  the  next  flood  the  holes  would 
be  filled  up  with  additional  stone,  and  this  process  repeated 
from  year  to  year  till  a  condition  of  absolute  stability  was 
reached. 

There  is  one  other  feature  about  this  Egyptian  weir  design 
which  is  worth  attention.  Down  stream  of  the  footing  wall  is 
an  arrangement  known  as  "  Beresford's  filter,"  so  named 
because  Mr.  J.  S.  Beresford,  C.I.E.,  was  the  first  to  suggest  its 
adoption  in  India.  It  is  an  inverted  filter  with  strata  of 
materials  of  gradually  increasing  size,  commencing  with  quite 
small  stone  at  t.he  bottom.  The  filter  allows  the  filtration 
water  to  pass  freely,  but  prevents  the  passage  of  sand.  The 
percolation  water  that  travels  under  the  work  thus  issues  harm- 
lessly. As  a  matter  of  fact,  the  dry  rubble  mass  between  the 
two  walls  also  acts  as  a  filter  bed,  as  the  little  percolation  water 
that  at  times  flows  over  the  footing  wall  has  been  observed  to 
be  absolutely  clear. 

There  are  no  under-sluices  associated  with  the  Egyptian 
weir,  but  a  lock  only  for  navigation.  Neither  has  it  any  crest 
shutters.  The  afflux  in  a  high  flood  is  almost  imperceptible. 

On  the  Indian  weirs  the  crest  shutters  take  various  forms, 
and  much  ingenuity  has  been  expended  on  their  designs.  They 
are  for  the  most  part  raised  by  hand  and  secured  in  a  vertical 


126  IRRIGATION. 

• 

position  by  tie-rods  fastened  to  the  crest  of  the  weir.  During 
the  flood  they  are  laid  flat  on  the  weir  crest  in  recesses  made  to 
receive  them,  so  that  the  flood  has  a  free  passage.  The  shutters 
of  some  designs  are  self-acting,  and  fall  flat  when  the  flood 
reaches  a  certain  level.  Fig.  36  shows  the  pattern  of  crest 
shutters  erected  on  the  Sone  weir.  The  under-sluices  have  also 
furnished  a  fruitful  field  for  inventive  minds.  There  are  in  use 
many  interesting  contrivances  for  rapid  opening  when  the  flood 
comes,  some  of  which  have  been  proved  by  actual  practice  to 
be  serviceable.  One  of  the  most  fascinating  arrangements, 
designed  by  Mr.  Fouracres,  has  been  fitted  to  the  under-sluices 
of  the  Sone  weir.  But  though  this  and  others  work  well, 
the  tendency  of  evolution  in  irrigation  methods  of  regulation 
is  the  reverse  of  that  which  prevails  in  the  animal  world. 
Complexity  of  structure  is  giving  way  to  simplicity  of  design, 
as  being  less  subject  to  derangement  and  more  reliable.  The 
system  which  now  finds  favour  is  that  of  wide  vents,  fitted 
with  gates  which  are  lifted  vertically  by  an  overhead  traveller 
running  on  rails  laid  along  girders  supported  on  the  tops  of  the 
piers  above  high-water  level.  The  gates,  of  which  there  are 
usually  two  in  each  vent,  run  in  cast  iron  grooves  built  in  the 
sides  of  the  piers.  Friction  is  reduced  by  means  of  rollers, 
either  fixed  to  the  gates  or  arranged  on  the  "  Stoney  "  system. 
Hitherto  the  vents  have  been  generally  20  feet  in  the  clear, 
though,  in  Madras,  "  Smart's  shutters  "  with  counter- weights 
have  been  erected  in  all  sizes  up  to  40  feet  in  length  by  12  feet 
in  height.  "  Stoney 's  shutters  "  are  now  being  preferred  to 
"Smart's."  Shutters  80  feet  broad  by  9  feet  high,  counter- 
balanced and  running  in  grooves  on  "  Stoney's  rollers,"  are  a 
feature  of  the  design  for  a  proposed  regulator  across  the  Penner 
river  in  India. 

The  principle  of  Stoney's  gates  is  shown  in  Fig.  37.  The 
gate  bears  on  [groups  of  rollers  mounted  in  hanging  frames. 
The  gate  moves  freely  on  the  rollers,  and  the  rollers  on  the 
recessed  faces  of  the  jambs,  so  that  friction  is  minimised.  It  is 


MEANS   OF   DRAWING  ON   THE   SUPPLY. 


127 


easily  understood  that  the  sluice  gate  travels  up  and  down  at 
twice  the  rate  of  the  roller  groups.  Therefore,  to  maintain  the 
correct  relative  positions  of  gate  and  roller  frame  under  all 
circumstances,  the  two  are  connected  by  means  of  a  wire  rope 
which,  passing  under  a  pulley  at  the  upper  end  of  the  roller 
frame,  has  its  two  extremities  fastened,  the  one  to  the  upper 


no   37, 


UPSTREAM 


W.L. 


STONEYS 
GATES 

DIAGRAM 
SHOWING 
PRINCIPLE 


SECTION 

TWQOUGW 

GAT  C 

DOWNSTREAM    W.L. 


SILL     or     SLUICE 


CTAUNCHINQ 


ROLLER* 


PART 

PLAN 


Direction^ 
°f  Pressure 


edge  of  the  gate  and  the  other  to  a  fixed  point  in  the  side  of  the 
sluice.  Thus,  as  the  gate  is  lifted  2  feet,  for  example,  the 
roller  frame  rises  I  foot. 

In  the  various  attempts  that  have  been  made  from  time  to 
time  to  devise  a  gate  that  would  work  with  a  rolling  instead 
of  a  sliding  contact,  the  difficulty  of  obtaining  a  water-tight 
closure  against  the  two  faces  of  the  sluice  has  made  itself  felt. 


128 


IRRIGATION. 


Mr.  Stoney  has  overcome  this  difficulty  in  a  way  that  is 
simplicity  itself.  In  the  angle  formed  by  the  edge  of  the  sluice 
gate  and  the  face  of  the  jamb  a  turned  bar,  attached  loosely  to  the 
top  of  the  gate,  is  allowed  to  hang  freely.  The  pressure  of  the 
water  forces  this  "  staunching  rod  "  into  the  angle  against  both 
the  sluice  gate  and  the  jamb,  and  a  perfectly  water-tight  joint  is 
thus  secured.1  The  weight  of  the  gate  is  sometimes  balanced  by  a 
counter-weight  to  increase  the  facility  of  moving  it ;  but, 
whether  counter- weights  are  provided  or  not,  the  gates  are 
manipulated  with  the  greatest  ease. 

The  system   of  vertically  lifted  gates  sliding  in  groves  was 
THE  DELTA    BARRAGE 
CHANNELS 


FIG     33 


introduced  into  Egypt  by  Lieut.-Col.  J.  H.  Western,  C.M.G., 
when  he  was  charged  by  the  Egyptian  Government  with  the 
restoration  of  the  Delta  barrage.  In  this  work  the  vents 
are  5  metres  (16  feet  5  inches)  wide.  The  same  system 
has  been  imitated  in  the  newly  constructed  barrages  of  Egypt 
at  Assiout,  Zifta  and  Esna.  This  type  of  river  regulator, 
which  has  been  classified  above  as  the  Egyptian  type,  will  now 
be  described. 


*  "The  Stoney  Patent  Sluice,"  by  Ransomes  and  Rapier. 


MEANS   OF   DRAWING   ON    THE    SUPPLY.  129 

The  Delta  barrage  is  the  prototype  of  the  Nile  regulators. 
It  is  made  up  of  two  separate  works,  one  on  either  branch  of 
the  river  close  below  its  point  of  bifurcation.  The  main  canals, 
which  distribute  water  to  the  Delta,  take  off  from  the  pool 
above  the  twin  regulators.  Fig.  38  shows  in  plan  the  general 
arrangement  of  these  works,  and  Plate  VI.  gives  a  general  view 
of  the  down-stream  face  of  the  regulator  across  the  head  of  the 
Rosetta  branch.  The  Delta  barrage1  has  a  history  of  much 
interest  to  irrigation  engineers.  Its  construction  was  com- 
menced in  1843  by  M.  Mougel,  its  French  designer,  when 
Mehemet  Ali  was  the  ruler  of  Egypt.  The  design  to  which  it 
was  built  is  shown  in  Fig.  39.  When  the  work  was  subjected 
to  a  small  head  in  1863  and  1867,  unmistakable  signs  of 
failure  appeared  in  the  form  of  cracks  and  displacements,  and 
the  barrage  was  forthwith  put  upon  the  sick  list.  The  failure 
was  due  to  "piping."  Runs  below  the  floor  were  developed 
under  the  influence  of  the  head  of  water,  and  the  sand  of 
the  foundation  bed  was  carried  away  by  the  flowing  water  till 
the  floor  lost  its  support  and  settled  down.  The  defects  arose, 
not  so  much  from  faulty  design,  as  from  careless  construction  of 
the  foundations.  Worried  by  the  impatience  and  impetuosity 
of  the  Viceroy,  Mougel  Bey's  workmen  laid  the  foundation 
concrete  in  running  water,  which  carried  away  the  mortar  and 
left  loose  stone,  without  any  binding  material,  through  which 
the  springs  of  the  river  bed  had  free  passage.  The  design,  if 
faithfully  executed,  was  not  much  at  fault.  The  floor  was 
amply  strong  to  resist  the  upward  pressure  due  to  the  head, 
but  its  breadth  was  perhaps  deficient ;  and  the  protection  given 
both  on  the  upper  and  lower  sides  of  the  flooring  was  inadequate. 
From  1867  to  1883  the  barrage  attracted  attention  by  reason 
only  of  its  imposing  superstructure,  but  it  failed  to  produce  any 
impression  by  its  performances,  for  it  was  weakest  where 
strength  was  most  needed.  In  1883  the  Director-General 

1  "The  Delta  Barrage  of  Lower  Egypt,"  by  Major  R.  H.  Brown. 
Published  by  the  Egyptian  Government. 


130 


IRRTGATTON. 


of  Irrigation  proposed  to  maintain  the   barrage   as   a   simple 

bridge,  and  to  provide  for  the  irrigation  of  Lower  Egypt  by  a 

system    of  pumping    stations.     But    in    this    year    Egyptian 

DELTA    BARRAGE 


CROSS     SECTION     OF      MASONRY 


FIG 
FLOOR 


39 


$»  —  > 

II 

.8UPER8TRUCTUI 

ie                          h 

BUMMER    W   V  -          j_| 

r' 

---ORIOllCAl                              FLOOR                ^ 

—  «•    -  4%  -                 ] 

« 
I 

f                         .      i     .  ....     r  113—  ' 

'  '      * 

, 

JC» 


IMPERMEABLE  PLATFORM        238  AFTER          ADDITIONS'" 

Scale 

LO      0      10  50  ,      100 


irrigation  came  under  the  control  of  Anglo-Indian  reformers, 
and  the  result,  so  far  as  the  barrage  was  concerned,  was  to  save 
it  from  rejection,  and  to  raise  it  to  be  the  head  of  the  corner 
in  the  building  up  of  a  restored  scheme  of  Egyptian  irrigation. 

The  principle  on  which  the  design  of  the  Delta  barrage 
restoration  was  based  was  the  same  as  that  which  was  followed 
in  the  case  of  the  Narora  and  Chenab  weirs  already  described. 
The  path  of  travel  for  the  percolating  water  was  lengthened  by 
the  addition  of  impermeable  aprons  of  masonry  up  and  down 
stream,  thereby  increasing  the  width  of  floor  from  34  metres 
(in  feet)  to  72 \  metres  (238  feet),  two-thirds  of  the  increased 
width  being  up  stream. 

But,  besides  adding  to  the  width,  it  was  necessary  to  lay  a 
sound  water-tight  surface  over  the  old  floor,  which  was  cracked 
and  pierced  by  springs  in  many  places  and  was  otherwise 
defective.  The  new  covering  was  made  of  Portland  cement 
concrete  1*25  metres  (4  feet)  thick,  over  which  was  laid  a  heavy 
pavement  of  dressed  Trieste  ashlar  stone  under  the  arches  and 
over  that  part  of  the  down-stream  apron  where  the  action  was 


MEANS  OF  DRAWING  ON  THE  SUPPLY.  131 

most  severe.  In  Plate  VI.  will  be  seen  where  the  new  floor  cover- 
ing was  raised  above  the  general  level  along  the  length  that  was 
found  most  defective.  A  row  of  piles  was  added  under  the  up- 
stream apron — an  addition  which  is  now  considered  a  mistake. 
After  the  completion  of  these  works,  when  the  barrage  was  hold- 
ing up  water,  springs  appeared  down  stream  of  a  certain  length 
of  the  floor.  The  line  up  stream  along  which  the  sources  of  these 
springs  lay  was  detected,  and  the  flow  stopped  by  dredging 
out  a  shallow  trench  along  the  upper  edge  of  the  up-stream 
floor  extension  and  forming  a  clay  apron  in  it  under  water,  the 
clay  being  consolidated  by  a  submerged  sledge  and  protected 
from  scour  by  a  surface  layer  of  cement  concrete  in  sacks. 

By  means  of  this  restoration  work  the  barrage  was  made 
capable  of  holding  up  a  head  of  4  metres  (13  feet),  as  was 
originally  intended,  and  the  consequent  effect  on  the  produce 
of  Lower  Egypt  was  eminently  satisfactory. 

In  the  next  chapter  it  will  be  told  how  the  foundations  of  the 
barrage  were  further  consolidated  by  means  of  cement  grout. 
After  this  last  operation  the  maximum  head  held  up  was  4*35 
metres  (14  feet).  While  subject  to  this  head  the  barrage 
showed  no  signs  of  being  unduly  strained. 

But,  though  the  barrage  had  now  been  made  to  do  no  more 
than  its  duty,  it  was  thought  unwise  to  subject  a  work  of  such 
vital  importance  to  as  much  even  as  4  metres  head,  if  there  was 
a  practicable  way  of  avoiding  it.  So  supplementary  weirs  were 
proposed  to  take  some  of  the  strain  off  the  barrage.  At  first  no 
more  than  this  was  suggested,  but  the  project  grew  during  the 
period  of  study  beyond  the  original  idea,  and  was  eventually  so 
expanded  that,  instead  of  the  associated  barrage  and  weir 
holding  up  4  metres  (13  feet)  between  them,  the  combination 
was  designed  to  hold  up  6*20  metres  (20  feet),  the  old  work 
being  allotted  3  metres  of  this  head  instead  of  its  original  4 
metres.  In  this  way  a  more  perfect  control  over  the  distribu- 
tion of  water  at  the  apex  of  the  Delta  has  been  obtained,  not 
only  in  summer,  but  also  in  flood  ;  while  ?t  the  same  time 

K  2 


132  IRRIGATION. 

greater  security  has  been  gained.  The  design  of  the  weir,  beinq 
of  the  Indian  type,  has  already  been  discussed  (Fig.  34).  The 
effect  produced  on  the  river  levels,  and  the  distribution  of  the 
head  between  the  barrage  and  its  weirs,  are  shown  in  the 
diagram  (Fig.  40).  The  photograph,  of  which  Plate  VI.  is  the 
reproduction,  was  taken  before  the  construction  of  the  weirs, 
when  the  barrage  was  holding  up  13  feet  head  of  water.  The 
action  of  the  weirs  now  ponds  up  water  over  the  barrage  floor 
so  that  the  talus  stones  are  never  visible.  On  the  Rosetta 
branch  of  the  Nile  the  subsidiary  weir  is  1,500  metres  (1,640 

DIAGRAM 

OF     WATER     LEVELS     AT     THE     DELTA      BARRAGE 

before  and    after   construction    of   the. 


fl 

W.L.   WITH     WEIR              b 

vy  w  9w  9m 
"A**"* 
^W.L.  IN     POND    BETWEEN 

f  1  Q       *U 

a 

Ul 

.R 

L.W.L.  VV  I  THOUT_  WEIR 

*"  L        ' 

'i   "ivf 

^^.  tf£ 

0 

8 
i 

>  BARRAGE     AND     WEIR       (      I 

J     ,WLwirHOUT    WE)R( 

«• 

S                                       i~'i     _    -,: 

1 

«\      L.W.L 

>  BELOW    Wu. 
^ 

yards),  and  on  the  Damietta  branch  500  metres  (550  yards), 
down  stream  of  the  barrage,  so  that  the  weirs  are  entirely 
separate  works  from  the  older  construction. 

Other  instances  of  the  Egyptian  type  of  regulator  have  been 
lately  built  at  Assiout  and  Esna,  in  Upper  Egypt,  and  at  Zifta, 
in  Lower  Egypt.  As  the  design  of  the  latter  is  practically  the 
same  as  the  Assiout  barrage  design,  but  modified  in  certain 
details  as  a  result  of  the  experience  gained  in  building  the  Upper 
Egypt  work,  the  cross  section  of  the  Zifta  barrage  is  selected  as 
an  example  of  the  most  recent  form  of  the  Egyptian  type  of  river 
regulator.  Fig.  41  gives  the  principal  dimensions.  It  will  be 


MEANS  OF  DRAWING  ON   THE  SUPPLY.  133 

observed  that  the  floor  has  a  diminished  thickness  down  stream 
of  the  piers,  as  the  hydraulic  pressure  upwards,  due  to  percola- 
tion, decreases  towards  the  down-stream  end  of  the  floor,  and 
the  floor  surface  beyond  the  piers  is  not  subject  to  the  pounding 
of  water  falling  over  the  gates.  The  clay  apron  up  stream, 
weighted  with  rubble,  forms  an  extension  of  the  impermeable 
floor,  and  removes  the  starting-point  of  the  flow  of  the  percola- 
tion water  to  the  up-stream  edge  of  the  clay.  Down  stream  of 
the  floor  is  an  inverted  filter  bed  overlaid  with  the  heavy  rubble 
of  the  talus.  Up-stream  and  down-stream  rows  of  piles,  with 
joints  grouted  up  solid  with  cement,  form  continuous  curtains. 

ZIFTA    BARRAGE 

CROSS  SECTION  OF  FLOOR 

FIG   41 


1 

1 

SUPERSTRUCTURE 

*  J 

5    " 

^Impermeable  - 

Platforwir  U-H&a-- 

j 
-—  —  ^ 

fccd 

&•*(  f  CLAY     -co  J^; 

Rl'BRLK       iVA  yr>XK  r  ^  

^^p^^^^335wS^^ 

fp 

^  f 

to    o     i 

5o»4t 

t»                            60 

•gf 
E=r=T  /%* 

The  up-stream  piles  are  useful  in  increasing  the  distance  the 
water  has  to  travel,  after  starting  from  the  up-  stream  edge  ot 
the  clay  apron,  before  it  presses  upwards  on  the  under  side  of 
the  floor.  'The  down-stream  piles  are  not  necessary  to  the 
finished  work,  but  they  facilitated  the  laying  of  the  concrete 
platform,  and  were  also  a  security  against  the  material  of  the 
river  bed  below  the  concrete  being  withdrawn  by  springs 
flowing  from  under  it  to  the  pumps  which  kept  the  water  down 
during  the  construction  of  the  floor.  The  down-stream  row  of 
piles  was  therefore  retained,  but  was  made  of  less  depth  than 
the  up-stream  line. 

It  was  found  during  the  construction  of  the  Assiout  barrage 


134  IRRIGATION. 

that  the  weak  point  was  the  line  of  junction  between  piles  and 
concrete,  along  which  springs  forced  their  way  upwards.  In 
the  Zifta  barrage  design  the  masonry  floor  was  therefore 
extended  outwards  for  a  short  distance  up  stream  and  down 
stream,  to  cover  the  heads  of  the  piles,  an  arrangement  which 
would  enable  the  springs  to  be  dealt  with  and  effectually  closed 
if  they  appeared. 

The  Zifta  barrage  was  designed  to  hold  up  4  metres  (13  feet) 
of  water,  which  it  proved,  after  construction,  to  be  fully 
capable  of  doing.  But  before  it  had  been  in  use  two  years,  the 
advantage  of  holding  up  more  than  4  metres  (13  feet)  was 
recognised,  and  a  subsidiary  weir  has  been  constructed  down 
stream  to  enable  the  heading  up  to  be  increased.  This  weir  is 
a  more  modest  one  than  the  Delta  barrage  weirs,  but  it  is  of 
much  the  same  design  to  a  smaller  scale. 

With  reference  to  the  question  of  the  future  type  of  river 
regulator  that  engineers  in  India  may  be  expected  to  adopt,  the 
following  passage  occurs  in  a  Manual  on  Irrigation  Works, 
compiled  by  Mr.  B.  P.  Reynolds,  Instructor  in  Civil  Engineer- 
ing, for  the  use  of  the  students  at  the  College  of  Engineering 
in  Madras,  India.  The  manual  is  dated  January,  1906,  and 
therefore  may  be  assumed  to  be  giving  expression  to  the  recent 
thought  of  engineers  in  India,  so  far  as  the  author  of  the  manual 
was  acquainted  with  it : — "  There  can  be  no  doubt  that  the 
weirs  of  the  future  will  be  of  the  open  type,  raised  little,  if  any, 
above  the  bed  of  the  stream  and  fitted  with  movable  shutters 
on  the  crest ;  and  since  it  is  necessary  that  some  kind  of  bridge 
should  be  erected  over  them  from  which  to  work  the  lifting  gear 
of  the  shutters,  it  follows  that  these  weirs  practically  become 
regulators.  In  almost  every  case,  except  perhaps  for  very 
broad  rivers,  the  shutters  will  be  of  the  lifting  type ;  falling 
shutters,  while  useful  for  broad  rivers,  have  the  serious  objec- 
tion that  once  they  fall  the  flood  water  must  drop  nearly  or 
quite  to  the  level  of  the  floor  of  the  weir  before  they  can  be 
raised  again,  while  with  lifting  shutters  the  water  can  be  held 


MEANS  OF   DRAWING  ON    THE   SUPPLY.  135 

up  to  any  convenient  height  and  all  excess  safely  passed." 
The  Zifta  barrage  is  an  embodiment  of  modern  ideas  as  to  the 
principles  on  which  a  river  regulator  should  be  designed,  and 
it  would  appear  from  the  passage  quoted  above  that  the  Indian 
type  is  likely  to  be  modified  in  such  a  way  that  it  may  even- 
tually differ  by  little,  if  at  all,  from  the  Egyptian  type.  The 
existing  barrages  of  Egypt  are  divided  into  bays  of  5  metres 
(16  feet  4  inches)  width,  and  have  their  floor  surfaces  flush  with 
the  bed  of  the  river.  With  the  facility  of  regulation  provided 
by  Stoney's  shutters  the  width  of  the  bays  could  without  incon- 
venience be  increased  four  or  five  times,  as  in  the  regulator 
across  the  Penner  river;  and,  if  ample  width  of  waterway 
were  allowed,  there  would  be  no  objection  to  raising  the  floor 
a  little  above  the  river  bed  with  the  object  of  decreasing  the 
height  of  shutter  required  to  hold  up  water  to  the  desired  level. 
Mr.  Buckley  ("  Irrigation  Works  in  India,"  p.  149)  describes 
the  method  of  remodelling  the  Coleroon  anicut  in  India.  The 
original  weir  proved  in  time  to  be  not  high  enough.  A  new 
"anicut"  was  therefore  built,  up  stream  of  the  old  one,  with 
fifty-five  40  feet  spans,  regulated  by  lift  shutters  4  feet  high. 
As  the  sill  of  the  new  "  anicut "  is  4  feet  below  the  crest  of  the 
old  weir,  the  top  of  the  shutters  is  only  2  feet  higher  than  the 
crest,  and  therefore,  if  the  sluices  in  the  old  weir  were  to  be 
wholly  closed,  the  new  work  would  have  only  a  2  feet  head  to 
support,  while  the  old  work  would  hold  up  4  to  5  feet.  This 
combined  work  has,  therefore,  a  resemblance  to  the  Egyptian 
Delta  barrage  and  its  weirs,  but  the  order  of  construction  of 
barrage  and  weir  was  reversed.  The  new  "anicut"  of  the 
Coleroon  combination  is  in  fact,  as  Mr.  Buckley  states,  "  an 
arched  bridge,  the  water  passing  through  it  being  regulated  by 
means  of  lift  shutters."  In  other  words,  it  is  a  river  regulator 
of  the  same  type  as  the  barrages  of  Egypt. 

Reference  has  been  made  in  the  earlier  part  of  this  chapter 
to  the  intention  of  the  Egyptian  Government  in  1883  to  adopt 
pumping  from  the  river  as  its  only  method  of  supplying  Nile 


I 

136  IRRIGATION. 

water  for  irrigation.  For  some  years  previously  pumping 
stations  at  Atfeh  and  Khatatbeh,  in  Lower  Egypt,  had  been  at 
work  lifting  water  from  the  Rosetta  branch  of  the  river  for  the 
irrigation  of  the  Western  Province  of  the  Delta.  A  contract 
had  been  concluded  with  a  company  for  the  wrorking  of  these 
stations,  the  terms  of  which  were  modified  in  1883  to  provide 
for  an  increase  in  the  amount  of  water  delivered  into  the  canals 
by  the  pumping  stations.  The  new  terms  provided  for  a  supply 
of  2,000,000  cubic  metres  a  day  (818  cubic  feet  a  second)  at 
Atfeh,  and  2,500,000  cubic  metres  a  day  (1,022  cubic  feet  a 
second)  at  Khatatbeh,  at  an  annual  cost  of  about  £50,000. 
This  contract  was  to  last  till  1915.  As  the  Delta  barrage  stood 
condemned  as  incompetent  to  serve  the  needs  of  irrigation,  it 
was  proposed  to  extend  the  same  system  of  supply  by  pumping 
to  the  whole  of  Lower  Egypt  at  an  initial  cost  of  £700,000  and 
an  annual  expenditure  of  £250,000.  But  fortunately  for  Egypt, 
before  a  decision  had  been  taken  regarding  this  proposal, 
Colonel  (now  Sir  Colin)  Scott-Moncrieff  was  entrusted  with  the 
management  of  the  irrigation  of  Egypt.  He  pigeon-holed  the 
pumping  project,  declared  himself  in  favour  of  a  restored 
barrage,  and  forthwith  took  steps  that  led  to  its  successful 
restoration. 

The  total  cost  of  the  restoration  was  £475,000.  About 
£500,000  more  was  spent  on  the  east  and  west  main  canals  to  fit 
them  for  their  work.  It  may  be  stated  in  round  figures  that  the 
barrage  restoration  project  cost  one  million,  and,  as  the  pumping 
project  was  estimated  to  cost  £700,000,  its  actual  cost  would 
probably  have  been  also  about  one  million.  But  when  a  com- 
parison is  made  of  the  annual  expenditure  in  each  case,  the  dif- 
ference is  striking.  The  Delta  barrage  costs  less  than  £10,000 
a  year  to  maintain  and  regulate,  and  without  any  further  expense 
is  capable  of  distributing  any  increased  supply  that  may  be 
provided  to  meet  the  demands  of  a  growing  area  of  cultiva- 
tion ;  whereas  the  annual  cost  of  lifting  the  water  by  pumps 
— estimated  at  £250,000  in  1883,  before  the  development  in 


MEANS   OF   DRAWING   ON    THE   SUPPLY.  137 

cultivation  of  the  past  twenty  years  had  taken  place — would 
increase  with  the  quantity  of  water  to  be  lifted,  and  fluctuate 
with  the  price  of  coal.  Moreover,  it  would  be  a  risky  thing  for 
Egypt,  whose  coal  supply  must  come  by  sea,  to  be  dependent 
on  imported  fuel.  In  time  of  war  the  coal  supply  might  be  cut 
off,  and  a  coal  famine,  of  two  months  duration  only,  would, 
under  such  circumstances,  be  enough  to  seal  the  fate  of  the 
growing  cotton  crop,  worth  £15,000,000  at  present  prices.  The 
barrage  is  undoubtedly  the  most  reliable  agent  for  Egypt  to 
entrust  with  her  interests.  It  has,  since  its  restoration,  become 
so  efficient,  and  is  so  unmistakably  the  proper  instrument  for  the 
water  distribution  of  the  Delta,  that  the  Khatatbeh  pumping 
station  has  been  dismantled,  and  its  engines  and  pumps  trans- 
ferred to  another  station  which  provides  for  the  drainage  of 
low-lying  lands  in  the  north-west  portion  of  the  Delta.  The 
Atfeh  pumping  station  is  still  maintained,  as  it  is  so  situated 
that  it  can  assist  in  supplementing  the  summer  supply  by 
pumping  into  the  Mahmudia  Canal  the  water  that  comes  from 
springs  and  percolation  in  the  river  trough  itself,  between  the 
barrage  and  Atfeh,  when  the  Delta  barrage  is  closed.  This 
source  of  supply  has  not  been  mentioned  in  Chapter  IV.  as  it 
is  peculiar  to  Egypt,  but,  as  similar  conditions  may  arise  else- 
where, it  may  be  worth  while  to  point  out  the  measures  taken 
in  Egypt  to  utilise  every  available  drop  of  river  water  in  its 
irrigation.  By  the  time  that  the  river  discharge  reaching  the 
Delta  barrage  has  so  far  decreased  that  it  is  no  more  than  that 
required  by  the  canals  fed  from  the  river  above,  the  gradual 
lowering  of  the  barrage  gates  is  complete.  The  leaks  round 
the  ends  and  between  the  gates  are  then  caulked  with  rags,  and 
the  closure  of  the  two  branches  of  the  river  by  the  barrage 
made  practically  water-tight.  But  below  the  barrage  there  are, 
on  each  branch,  some  200  kilometres  (125  miles)  of  channel 
from  the  beds  and  sides  of  which  spring  and  percolation  water 
collects  in  quantity  not  to  be  despised.  When  the  river 
discharge  is  due  to  this  source  alone,  the  salt  water  of  the 


138  IRRIGATION. 

Mediterranean  invades  the  lower  reaches  of  the  river  branches 
and,  mixing  with  the  spring  water,  renders  it  unfit  for  irrigation 
purposes.  Therefore,  in  order  to  make  this  spring  water 
available  for  irrigation,  the  engineers  have,  since  the  barrage 
became  efficient,  adopted  the  practice  of  constructing  tem- 
porary dams,  one  in  either  branch  some  little  distance  from  the 
point  where  it  joins  the  sea,  with  the  double  object  of  excluding 
the  salt  water  and  of  retaining  the  spring  water.  On  the 
Damietta  branch  this  water  is  drawn  upon  by  a  number  of 
privately  owned  pumps,  and  on  the  Rosetta  branch  by  a  few 
private  pumps  and  by  the  Government  pumps  at  Atfeh.  More 
than  half  of  the  supply,  however,  flows  by  gravitation  into 
canals  irrigating  low-level  lands  in  the  north  of  the  Delta.  The 
quantity  of  water  obtained  during  the  summer  by  such  means 
from  the  Rosetta  branch  is  generally  about  100,000,000  cubic 
metres,  though  as  much  as  170,000,000  is  reckoned  to  have 
been  obtained.  The  Damietta  branch  is  calculated  to  similarly 
supply  80,000,000  cubic  metres. 

The  Atfeh  pumping  station  is  the  only  remaining  Govern- 
ment station  in  Lower  Egypt  which  is  worked  in  the  interests  of 
irrigation.1  Its  performances  are,  moreover,  limited  to  lifting 
from  70,000,000  to  75,000,000  cubic  metres  during  the  summer 
when  the  want  of  water  is  most  felt. 

But,  though  the  irrigation  of  the  Delta  can  be  more 
economically  and  efficiently  done  by  a  system  of  canals 
depending  on  barrages  than  by  pumping,  there  are  certain 
isolated  areas  in  Upper  Egypt  which  cannot  be  given  perennial 
irrigation  without  pumping.  The  Egyptian  Government  has 
now  erected  pumping  stations  for  East  Giza,  a  tract  of  country 
comprising  about  46,000  acres  lying  immediately  to  the  south 
of  Cairo.  As  this  land  cannot  be  served  by  a  perennial  canal 
on  account  of  its  isolation,  there  was  no  choice  in  the  matter  if 
it  was  to  be  given  perennial  irrigation. 

1  The  previously  privately-owned  Abu  Menaga  pumping  station  has  been 
taken  over  by  the  Government  for  the  irrigation  of  12,000  acres  in  the  high 
level  province  of  Kaliubia.  The  prospective  area  to  be  served  is  68 ,000  acres. 


MEANS   OF   DRAWING   ON   THE  SUPPLY.  139 

In  Upper  Egypt  there  are  some  200  pumps  operated  under 
private  enterprise  by  engines  of  an  aggregate  horse-power  of 
about  5,000.  The  largest  among  these  are  worked  in  combina- 
tion with  sugar  factories,  for  the  irrigation  chiefly  of  sugar  cane. 
During  the  flood  season  they  are  relieved  by  the  inundation 
canals  whenever  these  latter  flow  at  a  sufficiently  high  level  to 
give  irrigation  by  "  free-flow."  The  following  are  the  five  most 
powerful  stations. 

Names  of  Stations,  Horse  power.  Area  of  Crop  Irrigated. 

Mataana.  150  1,500  acres 

Armant  ....  250  .  .  „  2,500  „ 
Dabaya  ....  150  ...  1,500  „ 
Naga  Hamadi  .  .  500  .  .  .  5,000  „ 
Ayat  ....  400  .  .  4,000  „ 


The  lift  in  summer  in  Upper  Egypt  is  from  8  to  10  metres 
(26  to  33  feet). 

There  is  an  interesting  venture,  undertaken  by  a  company, 
to  irrigate  the  Komombos  plain  in  Upper  Egypt.  The  soil  of 
the  plain  is  derived  from  the  high  ranges  which  skirt  the  Red 
Sea,  and  has  proved  to  be  productive  when  irrigated.  But  its 
surface  is  some  20  metres  (65  feet)  above  the  summer  level  of 
the  Nile,  and  half  that  height  above  high-flood  level.  At  this 
remote  point  the  price  of  coal  reaches  a  high  figure.  There  were 
originally  no  local  supplies  of  fuel,  as  the  plain  was  bare. 
Nevertheless  a  company  applied  for  and  obtained  a  concession 
for  the  reclamation  of  the  plain.  Three  pumps  of  1,500  I.H.P. 
each  (giving  each  1,000  horse-power  in  water  lifted)  lift  water 
about  24  metres  (78  feet)  for  the  irrigation  of  20,000  to  25,000 
acres.1  To  adapt  the  pumps  to  the  varying  conditions  of  river 
level  in  flood  and  summer  they  have  been  sunk  in  a  pit  about 
5  metres  (16  feet)  below  the  level  of  high  flood.  The  success 
of  this  undertaking  depends  upon  the  efficiency  of  the  pumps 
and  good  management,  for  the  conditions  are  formidable. 

1  A  iourth  pump  of  2,000  horse-power  has  been  added  as  a  reserve. 


140  IRRIGATION. 

Sir  William  Willcocks  in  "  Egyptian  Irrigation  "  estimates 
the  number  of  pumps  driven  by  steam  power  in  Egypt  at 
7,000,  with  an  aggregate  I.H.P.  of  57,000.  This  estimate 
probably  includes  the  pumps  used  for  drainage  purposes,  which 
will  be  referred  to  later. 

It 'is  rather  a  remarkable  fact  that  in  India,  at  the  beginning 
of  this  century,  not  an  acre  of  land  had  been  irrigated  by 
Government  otherwise  than  by  natural  flow.  In  so  large  a 
country,  where  all  sorts  of  conditions  exist,  there  must  be  land 
so  situated  with  reference  to  water  supply  that  pumping  must  be 
the  most  convenient,  if  not  the  only  possible,  way  of  irrigating  it. 
At  length  the  Madras  Government  recognised  this  in  a  particular 
instance,  and  approved  a  project  known  as  the  "  Divi  Pumping 
Project,"  which  provided  for  lifting  water  10  to  12  feet  for  the 
irrigation  of  50,000  acres.  The  pumping  station  consists  of 
eight  i6o-brake-horse-power  Diesel  oil  engines  and  Gwynne 
centrifugal  pumps  with  discharge  pipes  39  inches  in  diameter. 

The  cost  of  lifting  a  given  quantity  of  water  varies  naturally 
with  the  height  it  is  raised  and  with  the  price  of  fuel.  It  also 
varies  with  the  power  of  the  pumping  stations,  large  installations 
working  more  economically  than  small  ones.  The  question  of 
cost  will  be  examined  when  pumping  stations  for  drainage 
purposes  are  under  consideration. 


CHAPTER   VII. 

METHODS   OF   CONSTRUCTION. 

UNDER  the  head  of  Construction  the  irrigation  engineer  has 
to  deal  with  works  as  big  as  the  Assuan  dam  and  as  small  as  a 
field  outlet  of  a  few  inches  diameter.  Between  these  extremes 
lie  anicuts,  barrages,  canal  head  works,  weirs,  regulators,  locks, 
inlets,  escapes,  syphons,  aqueducts  and  culverts.  The  common 
characteristic  of  all  such  works  is  that  they  have  to  control  the 
flow  of  water  in  one  sense  or  another,  and  therefore  should  be 
built  of  materials  that  will  resist  the  action  of  water.  Other- 
wise the  ordinary  principles  of  construction  apply  to  them. 
Good  stone  and  brick  in  hydraulic  mortar  are  the  most  reliable 
materials.  Iron  can  be  safely  used  under  water  only  on  surfaces, 
and  for  those  structural  parts  which  can  be  periodically 
examined,  so  that  any  deterioration  may  be  detected  and  made 
good.  Wood  is  only  fit  for  use  in  temporary  works  and  for 
movable  parts  such  as  regulating  apparatus.  Some  hydraulic 
engineers  of  a  robust  faith  may  be  found  to  put  their  trust  in 
ferro-concrete,  or  ciment-arme ;  but  they  would  do  well  to 
remember  that  the  process  is  too  new  for  time  to  have  concluded 
its  course  of  object-lessons.  Those  who  are  interested  in  seeing 
what  daring  flights  of  design  the  advocates  of  this  system  are 
capable  of  making  should  turn  to  p.  4  of  Willcocks'  "  The  Nile 
Reservoir  Dam  at  Assuan  and  After."  ^ 

In  the  figures  illustrating  the  text  the  different  descriptions 

of  masonry  employed  in  any  work,  selected  as  an  example,  are 

not  distinguished  one  from  another,  as  the  choice  of  material 

depends  generally  on  local  resources.     In  Chapter  VI.,  p.  116, 

.shlar  was  mentioned  as  a  good  covering  for  floors  which  are 


142  IRRIGATION. 

subjected  to  the  impact  of  falling  water,  with  the  proviso, 
however,  that  the  ashlar  must  be  properly  bedded.  In  Mr. 
Buckley's  account  of  the  failure  of  the  Narora  weir,  quoted  on 
p.  118,  it  is  stated  that  a  strong  spring  passed  under  the  stone 
flooring  and  lifted  it  bodily  over  a  length  of  340  feet  Now 
this  could  not  have  happened  if  the  ashlar  had  been  properly 
bedded.  There  must  have  been  unfilled  spaces  between  the 
ashlar  covering  and  the  floor  below  it,  over  which  the  water 
pressure  acted.  Assuming  that  the  vertical  joints  of  the  ashlar 
were  perfectly  filled,  and  that  the  bed  joints  were  imperfectly 
filled,  and  also  that  the  sub-ashlar  spaces  were  in  communica- 
tion with  the  up-stream  head  of  water  by  ever  so  small  a  channel, 
the  ashlar  would  be  in  danger  of  being  lifted  if  the  void  spaces 
and  head  of  water  were  great  enough  to  develop  the  pressure 
necessary  to  overcome  the  weight  of  the  stone.  Supposing  this 
were  so  and  the  ashlar  blown  up,  the  remaining  thickness  of 
floor,  below  the  ashlar,  might  then  be  too  weak  to  resist  the 
upward  pressure  of  percolation  water  from  below,  and  a  failure 
of  the  work  would  result  by  the  rupture  of  the  floor.  In  con- 
sequence of  this  objection  to  ashlar,  namely,  the  difficulty  of 
securing  a  perfectly  uninterrupted  bond  between  the  ashlar  and 
the  masonry  below  it,  it  is  sometimes  considered  preferable  to 
dispense  with  an  ashlar  covering  and  to  build  the  floor  of 
homogeneous  material.  The  floors  of  both  the  Assiout  and  Zifta 
barrages  in  Egypt  were  so  built,  the  material  of  the  floor  above 
the  bed  layer  of  concrete  being  of  rubble  stone  in  3  to  I  cement 
mortar  throughout.  All  the  stones  were  laid,  as  far  as 
possible,  with  their  longest  dimensions  vertical,  so  as  to  obtain  a 
vertical  bond.  The  masonry  was  brought  up  rough  to  floor 
level,  and  was  surfaced  by  laying  fine  concrete  (2  stone,  I  sand, 
i  cement)  between  the  projecting  points  of  the  rubble  masonry. 
All  points  of  stones  that  projected  above  the  correct  floor- 
surface  level  were  dressed  off  with  a  stone-dresser's  hammer. 

So  far  as  the  foundations  of  most  of  the  larger  works  are  con- 
cerned, the  methods  of  execution  are  those  which  are  imposed  by 


METHODS   OF  CONSTRUCTION.  143 

the  necessity  of  building  below  the  level  of  lowest  water.  The 
nature  of  the  foundation  bed,  and  the  strength  of  the  springs 
over  the  foundation  area,  are  important  matters  for  considera- 
tion in  selecting  the  method  to  be  adopted.  But  the  price  of 
materials  and  facilities  for  obtaining  them,  as  also  the  quality 
of  the  labour  market  and  the  nature  of  engineering  plant  avail- 
able, have  to  be  taken  into  account.  In  the  case  of  works  to 
be  built  on  rivers  which  are  in  flood  during  certain  months  of 
the  year,  or,  in  countries  where  a  rainy  season  interferes  with 
construction,  the  duration  of  the  working  season  also  will  influ- 
ence the  decision  as  to  the  most  convenient  method  to  adopt. 

If  the  springs  of  the  foundation  bed  are  not  expected  to  be 
too  powerful  to  be  dealt  with  by  the  pumps  which  can  be 
brought  to  site,  the  ordinary  method  of  getting  in  foundations 
below  spring  level  is  to  surround  the  area  of  operations  by 
banks  so  as  to  exclude  the  outside  water  (if  the  foundation  pit 
is  not  otherwise  enclosed),  and  to  get  rid  of  the  inside  water  by 
pumping.  It  may  sound  a  simple  matter  to  surround  the  area 
by  banks  capable  of  excluding  the  outside  water,  but  in  some 
cases  this  operation  is  a  very  formidable  one,  on  the  success  of 
which  the  whole  work  depends.  The  enclosing  banks  should 
be  made  well  clear  of  the  outside  limits  of  the  foundation  area, 
with  a  good  margin  to  spare  to  allow  for  the  earthwork  settling 
down  to  a  broader  base  under  the  action  of  percolation,  which 
will  increase  as  the  inside  water  is  lowered  by  pumping. 
Interior  space  is  also  useful  as  affording  room  for  stacking 
materials,  and  for  the  erection  of  pumps  with  their  wells.  The 
wells  for  pumps  should  be  outside  the  extreme  limits  of  the 
permanent  work.  The  pumps  keep  the  water  level  in  the 
enclosed  area  low  while  the  excavation  of  the  foundation  pit 
is  carried  down  to  full  level  and  the  masonry  of  the  foundation 
is  laid,  so  to  speak,  in  the  dry.  As  the  bed  on  which  the  bottom 
concrete  is  laid  is  often  covered  with  several  inches  of  water, 
wherever  springs  are  numerous,  a  liberal  allowance  of  cement 
must  be  used  in  mixing  the  concrete. 


144  IRRIGATION. 

One  advantage  of  this  method  over  others  is  that  all 
the  work  done  is  in  sight  at  the  time  of  execution,  and 
it  can  therefore  be  supervised  the  more  efficiently.  But  it 
has  this  disadvantage,  namely,  that,  unless  the  springs  are 
intelligently  and  skilfully  treated,  defects  in  the  foundations 
will  be  created  by  the  water  forcing  its  way  either  under  or 
through  the  masonry.  It  happens  sometimes  that  the  super- 
vising staff  has  not  the  experience  necessary  for  successfully 
dealing  with  the  springs,  but  gains  it  as  the  work  proceeds,  so 
that  the  first  season's  work  is  not  without  its  mistakes.-  The 
golden  rule  to  be  observed  in  dealing  with  springs  is  that  no 
attempt  should  be  made  to  stop  them  working  until  they  have 
been  surrounded  on  all  sides  by  masonry  of  sufficient  strength 
to  resist  their  efforts  to  find  a  new  outlet  under  or  through  it. 
In  the  case  of  any  work  of  similar  design  to  that  of  the  Zifta 
barrage  (Fig.  41),  if  the  cement  concrete,  which  forms  the 
bottom  layer  of  the  foundation  platform,  is  advanced  from  one 
extremity  of  the  work  in  an  even  line  towards  the  other, 
regardless  of  what  springs  it  may  meet  with,  the  springs  will 
form  runs  for  themselves  through  the  unset  edge  of  the  concrete 
layer.  And,  as  the  work  advances,  more  and  more  springs  will 
assert  themselves  in  the  same  way,  until  there  is  a  strong 
out-flow  along  the  advancing  edge  of  the  concrete,  due  to  the 
combined  action  of  all  the  springs  encountered ;  except  such  as 
may  have  forced  their  way  side- ways  to  the  lateral  margins  of 
the  concrete  layer  and  have  found  for  themselves  a  free  outlet 
there.  The  cementing  material  of  the  concrete  will  thus  be 
washed  away  as  soon  as  it  is  laid,  and  runs  will  be  formed 
under  and  through  the  foundation  platform,  which  will  be 
sources  of  trouble  afterwards.  The  way  to  avoid  this  is 
carefully  to  locate  all  springs  in  advance  of  the  work,  and  to 
carry  the  concrete  round  them,  but  not  over  them.  Thus  the 
springs  will  continue  to  work  unmolested.  But,  in  order  to 
prevent  the  discharge  from  them  interfering  with  the  progress 
of  the  work  elsewhere,  their  water  must  be  confined  and  led 


METHODS  OF  CONSTRUCTION.  145 

away  in  pipes  or  channels  of  set  masonry  over  or  through  the 
concrete  layer,  and  be  allowed  to  flow  until  the  sources  are 
completely  surrounded  by  masonry  too  strong  for  the  springs 
to  burst  through  They  can  then  be  forcibly  stopped  with  safety, 
and  be  rendered  powerless  to  work  harm  ,  The  methods  of 
dealing  with  springs  vary  in  detail  with  the  ingenuity  of  those  in 
charge  of  the  work,  but  the  guiding  principle  is  the  same  in  all 
cases,  namely,  to  offer  no  violence  to  the  spring  till  sufficient  forces 
are  marshalled  and  the  investment  is  so  complete  as  to  make 
any  attempt  to  break  out  hopeless  and  submission  inevitable. 

The  method  of  enclosing  the  foundation  area  and  keeping  the 
inside  water  down  by  pumping  was  recently  adopted  in  Egypt 
for  the  construction  of  the  Assiout  and  Zifta  barrages,  as  it  was 
also  some  years  previously  for  the  restoration  works  of  the 
Delta  barrage. 

The  Delta  barrage  restoration,  carried  out  under  the 
direction  of  Col.  J.  H.  Western,  C.M.G.,  was  a  work  of  much 
difficulty.  The  barrage,  as  has  been  already  stated,  consists  of 
two  regulators,  one  across  the  head  of  each  of  the  two  branches 
into  which  the  Nile  divides  at  the  apex  of  the  Delta.  The 
regulator  across  the  Rosetta  branch  has  sixty-one  openings  of  5 
metres  (16  feet  5  inches)  and  two  locks,  and  is  465  metres  (1,525 
feet)  long  between  the  flanks.  The  regulator  across  the  Damietta 
branch  had  originally  seventy-one  openings  and  two  locks 
(reduced  during  the  restoration  to  sixty-one  arches  and  one  lock), 
and  was  535  metres  (1,755  feet)  long.  To  carry  out  the  restora- 
tion work  it  was  necessary  to  enclose  half  of  one  regulator  at  a 
time,  leaving  the  waterway  of  the  other  half  unobstructed  to  pass 
the  river  discharge ;  so  that  the  work  had  to  be  spread  over 
four  seasons/  The  working  season  between  two  successive 
floods  extended  from  November  to  June.  Four  months  of  this 
time  were  occupied  in  making  the  enclosing  banks  and  in 
pumping  out  and  clearing  the  area  of  work.  At  one  point  the 
enclosing  bank  had  to  be  made  in  a  maximum  depth  of  water 
of  15  metres  (49  feet).  When  the  pumping  had  lowered  the 

I.  L 


146  IRRIGATION. 

inside  water  sufficiently  to  allow  of  the  masonry  work  being 
carried  on,  the  head  of  water  against  the  up-stream  bank  was 
5*25  metres  (17  feet).  As  the  river  bed  was  sand,  so  great  a 
head  naturally  gave  rise  to  strong  springs  inside  the  enclosure, 
not  only  outside  the  limits  of  the  t  arrage  platforms,  but  also, 
in  consequence  of  original  defects  in  construction,  through 
cracks  and  runs  in  the  floor  itself.  In  one  instance  a  crack 
had  opened  out  into  a  fissure  4  inches  wide  for  a  length  of 
about  13  feet.  According  to  the  report  of  the  resident  engineer, 
Mr.  A.  G.  Reid,  "  where  cracks  of  this  sort  occurred  they  were 
staunched  as  follows :  the  broken  floor  was  cleared  of  debris 
bit  by  bit  and  covered  at  once  with  sand  to  a  depth  sufficient  to 
keep  down  the  springs.  It  was  then  surrounded  at  a  distance 
by  concrete  laid  after  thorough  clearing  on  the  sound  floor  and 
carried  up  to  a  level  at  which  the  springs  could  not  break 
through  it.  The  concrete  was  then  pushed  on  inwards  until  it 
was  stopped  by  the  flow  of  water.  When  this  occurred  the 
sand  was  carried  away  as  deep  as  possible,  and  rubble  masonry 
laid  in  cement  mortar  was  built  on  the  sand,  a  trench  about  5 
metres  wide  being  left  coinciding  with  the  crack  in  the  floor. 
Concrete  metal  was  laid  a  few  inches  deep,  and  on  it  a  pipe  2 
metres  longer  than  the  crack,  closed  at  one  end  and  perforated 
with  half-inch  holes  along  its  under  half-circumference  for  so 
much  of  its  length  as  coincided  with  the  crack,  was  securely 
built  into  the  new  masonry  for  its  imperforate  length.  An 
outflow  drain  was  left  in  the  masonry  in  the  prolongation  of 
the  pipe,  and  the  water  from  the  broken  floor  was  thus  passed 
through  the  pipe  to  the  pumps.  When  the  masonry  had  set, 
the  pipe  was  covered  in  with  masonry  laid  in  cement  gauged 
neat,  and  the  whole  then  raised  to  a  safe  height.  The  end  of 
the  pipe  was  afterwards  closed  with  an  iron  plate  and  the 
outflow  channel  built  up." 

The  manner  of  dealing  with  the  springs  met  with  in  the 
worst  opening  of  all,  where  it  was  found  necessary  to  build  the 
new  floor,  overlying  the  old,  with  a  surface  some  3  metres 


METHODS  OF  CONSTRUCTION.  147 

(10  feet)  higher  than  that  of  the  original  floor,  is  thus  described 
in  the  same  report  :  "  The  springs  under  this  arch  were 
numerous  and  prevented  the  water  being  got  down  below 
2  metres  above  floor.  They  were  closed  by  the  aid  of  iron 
pipes.  The  floor  having  been  cleared  of  debris,  silt  and  rubbish 
as  far  as  possible,  ordinary  cast  iron  pump  pipes,  6  feet  long, 
were  put  into  place,  one  vertically  over  each  spring,  and 
concrete  was  tipped  to  water  surface  round  them  and  over  the 
whole  area  of  the  floor.  Whilst  this  was  being  done,  the  water 
coming  through  the  pipes  was  led  away  to  the  pumps  in 
troughs  and  by  channels  previously  prepared.  When  the 
concrete  had  set  for  six  days,  a  trench  i  metre  wide  and 
extending  from  pier  to  pier  was  dug  through  the  concrete  down 
to  floor  level,  a  site  having  been  chosen  which  was,  as  far  as 
could  be  judged,  sound.  The  floor  was  thoroughly  cleansed, 
and  the  trench  was  then  filled  in  with  concrete  laid  in  layers 
and  rammed.  The  object  of  this  was  to  make  a  water-tight 
diaphragm  extend  from  the  old  to  the  new  floor,  and  thus  to 
prevent  creep  of  water  between  the  two.  The  pipes  were  then 
filled  with  finely  broken  concrete  metal  and  closed  by  quarter- 
inch  iron  plates  bolted  on  to  their  flanges,  indiarubber  packing 
rings  being  used  to  make  the  joint  tight.  The  whole  floor  was 
then  concreted  over  to  the  necessary  height  and  the  ashlar 
face  laid." 

But  the  greatest  source  of  trouble  were  the  numerous  springs 
which  found  their  way  upwards  between  the  piles  of  the  original 
rows  of  piling  within  which  the  floor  had  been  built.  Each 
separate  jet  had  to  be  led  into  a  pipe  of  suitable  size  surrounded 
with  masonry,  and  the  pipe  closed  and  built  over  after  the 
masonry  had  set.  As  the  manner  of  dealing  with  springs  is  of 
such  importance,  the  soundness  of  foundations  depending  on 
their  successful  treatment,  Sir  William  Willcocks'  description 
of  the  means  adopted  to  imprison  the  springs  along  the  old 
sheet  piling  of  the  barrage  is  worth  quoting  ("  Egyptian 
Irrigation  ").  See  Figs.  42  and  43. 

L  2 


148 


IRRIGATION. 


M  i.  Vertical  Pipes. — The  spring  was  dug  out  to  a  depth  of, 
say  30  centimetres  below  the  surface  of  the  old  masonry,  and  a 
vertical  tube  of  from  5  to  10  or  15  centimetres  diameter,  accord- 
ing to  the  quantity  of  the  water,  was  inserted.  The  hole  was 
then  filled  up  with  ballast  round  the  tube.  This  tube  was 
drilled  with  holes  on  the  lower  half  of  its  length,  while  at  the 
upper  end  were  cut  the  threads  of  a  screw,  so  that  a  cap  might 

METHODS 
OF    CLOSING     SPRINGS 


FIG 


PLAN 


METHOD 
BY 

VERTICAL 
PIPES 


METHOD 

G 

43 

BY 

HORIZONTAL 

PIPES 

D        E    F 

Nliff 

HKKK 

5 

CBMXVT 

r-.        tfASOStRX 

tH 
CLAY 

t     5 

*  o 

AS    "" 

P 

.             '.          *.      J                 1 

u  1      1 

«  ''"Iv.i  ^"*- 

'  -o_--jV 

eventually  be  screwed  on.  Round  the  pipe,  and  removed  about 
10  centimetres  from  it,  a  ring  of  brickwork  in  stiff  clay  was 
built,  open  on  one  side  ;  the  cement  masonry  was  then  brought 
up  from  A  and  B  till  it  was  flush  with  the  brickwork  in  stiff 
clay,  and  was  allowed  time  to  set.  When  set,  the  brickwork 
in  clay  was  removed,  and  the  space  between  the  pipe  and  the 
cement  masonry  was  filled  up  with  cement  mortar,  or  concrete 
or  brickwork,  an  open  space  being  still  left  on  ,  nc  side  to  allow 


METHODS  OF  CONSTRUCTION.  149 

the  water  coming  up  through  the  ballast  to  flow  freely  away. 
When  the  cement  mortar  had  thoroughly  set,  and  was  strong 
enough  to  prevent  springs  working  up  through  it,  the  opening 
was  quickly  shut  up  with  dry  cement  and  cement  mortar,  and 
weighed  down,  and  the  water  began  to  flow  freely  through  the 
top  of  the  pipe.  When  the  cement  closing  the  opening  had 
thoroughly  set,  the  cap  was  screwed  on  the  pipe  and  the  whole 
built  over. 

"  2.  Horizontal  Pipes. — The  pipe  in  this  case  was  drilled  with 
holes  on  half  the  circumference  of  half  the  length,  i.e.,  on  a 
quarter  of  its  surface,  and  was  laid  horizontally  in  a  trench, 
with  the  holes  over  the  spring,  which  had  already  had  ballast 
strewn  over  it.  The  ballast  was  spread  round  half  the  pipe  to 
the  axis  B  C.  At  E  F  a  ring  of  brick  in  stiff  clay  was  built 
round  the  pipe,  and  at  D  E  cement  masonry  round  the  pipe. 
When  the  masonry  at  D  E  had  set  thoroughly,  the  brickwork 
in  clay  was  removed  and  replaced  by  cement  mortar  or  brick- 
work, while  the  space  from  B  to  C  was  covered  with  cement 
mortar  and  masonry,  and  the  water  allowed  to  flow  down  the 
pipe  C  B  A.  Great  care  had  to  be  taken  that  a  hand  pump 
kept  the  water  at  M  always  lower  than  the  top  of  the  pipe, 
until  the  masonry  above  B  C  had  thoroughly  set.  When  the 
masonry  had  set  the  cap  A  was  screwed  on,  and  the  whole 
space  carefully  built  over  in  cement  masonry." 

The  Assiout  barrage,  in  Upper  Egypt,  spans  the  undivided 
river  as  a  regulator  with  in  openings  of  5  metres  (16  feet 
5  inches)  each  and  a  lock,  making  up  a  total  length  between 
abutment  faces  of  820  metres  (2,690  feet).  The  laying  of  the 
foundations  was  complete  in  three  working  seasons,  a  different 
section  of  the  work  being  enclosed  each  season,  while  the  river 
discharge  was  allowed  to  pass  in  the  other  sections.  The 
maximum  height  of  the  enclosing  bank  was  9*8  metres 
(32  feet  2  inches).  The  head  of  water  against  it,  when  the 
inside  water  had  been  pumped  down  to  the  required  level, 


1 50  IRRIGATION. 

varied  from  470  metres  (15  feet  5  inches)  to  6*25  metres 
(20  feet  6  inches).  The  bed  of  the  river  was  sand,  and  the 
whole  foundation  bed  was  alive  with  springs.  The  most 
suitable  pumps  for  unwatering  the  foundations  were  12-inch 
direct  acting  centrifugals  ;  larger  pumps  were  found  unwieldy, 
and  smaller  pumps,  though  useful  for  small  areas  on  account  of 
their  portability,  proved  unsuitable  for  use  as  main  pumps.  At 
one  time  there  were  seventeen  12-inch,  two  lo-inch,  six  8-inch, 
and  three  6-inch  centrifugal  pumps  at  work.  The  main  pumps 
were  mounted  in  pairs  on  circular  brick  wells,  5  feet  in 
diameter,  sunk  to  a  suitable  depth  just  outside  the  line  of 
the  pitching,  and  sealed  at  the  bottom  with  concrete  plugs. 
Apertures  to  admit  the  water  to  the  wells  were  made  in  their 
sides  at  successively  lower  levels  as  the  water  level  in  the 
foundation  pit  was  reduced.1 

The  springs  were  dealt  with  in  various  ways,  in  accordance 
with  the  principles  laid  down  above.  But  the  final  closing  of 
the  pipes,  to  which  the  springs  had  been  confined,  was  not 
done  as  at  the  Delta  barrage.  Provision  was  made  for  screwing 
on  other  pipe  lengths  to  a  height  of  5j  metres  (18  feet)  above 
the  floor,  so  that,  when  the  masonry  had  set,  each  spring  might 
be  forced  backwards  by  a  column  of  cement  grout,  and  any 
run  or  cavity  created  by  the  flow  of  the  spring  be  filled  by  the 
grout-  As  the  springs  were  so  numerous,  causing  an  outflow 
at  the  advancing  edge  of  the  concrete,  it  was  frequently  neces- 
sary to  stop  any  further  advance  and  to  recommence  the  work 
at  a  fresh  point  some  distance  ahead,  whence  the  concrete  was 
carried  back  to  meet  the  arrested  portion.  Large  openings 
were  temporarily  left  along  the  line  of  meeting  as  vent-holes  for 
the  springs,  which  were  then  controlled  and  finally  extinguished 
by  the  employment  of  perforated  pipes  and  cement  grout  under 
pressure. 

It  is  now  recognised  that  the  use  of  sheet-piling  of  the  ordinary 

i  "  The  Barrage  across  the  Nile  at  Asyut,"  by  G.  H.  Stephens.  Pro- 
ceedings InstC.E.,  Vol.  CLVIII.,  1904. 


METHODS   OF  CONSTRUCTION.  151 

description  to  form  curtains  is  a  mistake,  as  experience  gained 
at  the  Delta  barrage  and  elsewhere  has  taught  that  the  unfilled 
joints  form  so  many  leads  to  bring  deep-seated  springs  to  founda- 
tion level,  while,  in  consequence  of  these  joints,  the  advantage 
of  a  continuous  deep  curtain  wall  is  lost.  To  obviate  these 
objections  a  special  form  of  pile,  which  provides  for  the  complete 

CAST    IRON     PILES 


I  Q      44 


IDE     ELEVATION 

1 

f~ 

> 

j 

i 
i 

^s 

1 

i 

? 

>        E 

,    * 

S-  — 

,;> 

2     ^^ 

9 

PLAN 


CNLARGED        CROSS        SECTION 


rilling  of  the  joints  with  impervious  material,  was  adopted  at 
Assiout  and  Zifta.  This  pile  is  of  cast  iron,  with  a  tongue 
and  groove  arrangement  by  which  one  pile  locks  with  another. 
The  groove  is  deeper  than  the  length  of  the  tongue,  so  that, 
when  two  piles  are  locked  together,  there  remains  a  space 
between  the  end  of  the  tongue  and  the  back  of  the  groove,  into 
which  a  small  tube  can  be  inserted  (Fig.  44).  After  the  piles 


IRRIGATION. 


are  driven  and  the  pile-driver  has  advanced  to  a  safe  distance 
a  tube  is  introduced  into  the  groove  space  and  water  turned 
on  under  a  head.  The  jet  of  water  clears  out  the  sand  in  the 
joint,  and,  as  it  does  so,  the  nozzle  of  the  tube  descends  to  the 
bottom  of  the  joint.  The  water  is  then  turned  off  and  cement 
grout  substituted  (Fig.  45).  The  tube,  with  its  nozzle,  is  then 

•GROUTING    APPARATUS 

FOR      PILE       JOINTS 

I     ^ 


Scafe  oj 


r  IG    <s 


OhOUT     TANK 


TAP    FOP 

WATER 


TAP     F0f»     GROUT 


gradually  lifted  out  of  the  joint,  leaving  it  full  from  top  to 
bottom  of  cement  grout,  which  in  a  few  hours  sets  hard  enough 
to  resist  the  strongest  spring.  In  this  way  a  continuous  curtain, 
without  open  joints,  is  obtained  along  the  line  of  piles. 

The  piles  are  driven  as  soon  as  the  excavation  is  sufficiently 
advanced  for  the  pile-drivers  to  get  to  work,  so  that  the  piling 
is  complete  before  the  bottom  layer  of  the  excavation  is 
cleared. 


METHODS  OF   CONSTRUCTION.  153 

The  disadvantages  of  putting  in  foundations  with  strong 
springs  in  action  over  the  foundation  bed  have  caused  other 
methods  to  be  resorted  to.  The  system  which  makes  use  of 
compressed  air  is  well  suited  to  subaqueous  work  in  which 
depth  of  foundation,  but  not  continuity,  is  required.  The 
sinking  of  cylinders,  for  instance,  to  act  as  foundations  for  the 
girder  supports  of  river  bridges  is  frequently  effected  by  this 
method.  But  it  is  not  so  conveniently  applied  to  the  con- 
struction of  works  which  have  to  withstand  a  head  of  water 
and  require  continuous  foundations  of  unvarying  depth  without 
intervals.  Moreover,  the  system  requires  special  plant  of  a 
somewhat  complicated  order,  and  trained  labour  skilled  in  the 
process,  as  there  is  much  danger  attending  its  employment  by 
untrained  hands. 

In  India  the  method  of  getting  in  foundations  by  well- 
sinking  is  in  favour,  and  has  been  repeatedly  employed  with 
much  success.  Where  a  curtain  wall  has  to  be  formed  in  sand 
or  silt  below  spring  level,  it  is  most  unwise  to  attempt  to  get 
it  in  by  lowering  the  water  by  pumping  below  the  general 
foundation  level.  Well-sinking  is  one  method  of  avoiding  the 
necessity  of  doing  so,  A  group  of  wells  is  also  often  sunk  to 
provide  extra  support  for  heavy  lock  walls,  piers,  or  other  parts 
of  the  superstructure  requiring  greater  depth  of  foundation 
than  is  given  to  the  lighter  portions  of  the  work.  Well-sinking 
may  be  carried  out  with  the  help  of  compressed  air,  but  it  is 
usually  done  by  excavating  the  sand  or  soil  from  the  interior 
by  ordinary  dredging  plant.  Wells  may  be  circular  or 
rectangular.  Curbs  with  sloping  under-sides  and  outside 
cutting  edge  are  first  bedded  in  the  sand  or  soil  at  the  natural 
water  level,  or  at  the  level  to  which  it  may  be  judged  con- 
venient to  lower  the  water  by  pumping.  The  wells  are  built 
on  the  curbs,  and  the  masonry  given  time  to  set.  They  are 
then  weighted,  and  the  sand  dredged  from  within  by  special 
plant,  so  that  the  wells  gradually  sink  below  water  level  as  the 
excavation  continues.  More  height  is  added  to  them  (if  not 


1 54  IRRIGATION. 

originally  built  to  full  height),  and  the  sinking  is  continued 
till  the  bottom  of  the  well  has  reached  the  required  depth. 
Cement  concrete  is  then  lowered  to  the  bottom  of  the  well,  and 
a  plug  of  4  or  5  feet  thickness  formed ;  or  the  plug  may  be 
made  by  cement  grouting  if  the  water  in  the  well  is  allowed  to 
stand  at  spring  level  while  the  grouting  is  being  done.  When 
the  plug  has  had  time  to  set  the  interior  water  is  pumped  out, 
and  the  well  filled  with  ordinary  concrete,  or  even  simple  sand, 
as  the  interior  core  does  no  work.  The  intervals  between  wells 
are  then  cleared  out  as  far  as  possible  and  filled  with  concrete. 
The  superstructure  is  afterwards  built  on  a  platform  covering 
the  wells. 

In  the  construction  of  the  Sone  weir  in  India,  for  example, 
well-sinking  was  extensively  used  for  the  foundations  of  the 
weir  walls  and  under-sluices.  The  under-sluice  piers  and  the 
entire  floor  of  the  under-sluices  (which  is  537  feet  by  123  feet 
in  area)  are  founded  on  rectangular  blocks  or  wells,  generally 
8  feet  square,  which  are  sunk  all  over  the  area  to  a  depth 
of  about  8  feet ;  the  blocks  under  the  piers  are  longer  and 
deeper.  The  wells  are  filled  with  concrete  and  covered  with 
masonry  topped  with  ashlar  18  inches  thick  (Buckley). 

An  excellent  example  of  the  use  of  wells  for  foundations  is 
furnished  by  the  new  Nadrai  aqueduct  in  India  (see  Fig.  60, 
Chapter  IX.).  The  piers  which  carry  the  aqueduct  are  founded 
on  wells  sunk  52  feet  below  the  bed  of  the  lower  channel.  For 
such  foundations  as  these  well-sinking  is  a  most  useful  and 
efficient  system. 

The  sinking  of  foundation  wells  is  sometimes  a  troublesome 
and  tedious  operation,  especially  if  the  supervising  staff  and  the 
labour  employed  have  not  acquired  skill  by  previous  experience. 
What  to  do,  and  what  not  to  do,  to  ensure  that  the  wells  may 
sink  vertically  and  uniformly,  is  only  to  be  learnt  by  actual 
practice. 

The  great  objection  to  the  use  of  wells  for  the  foundations  of 
a  weir  core  wall,  or  for  a  curtain  wall  of  a  work  which  is 


METHODS   OF   CONSTRUCTION.  155 

subjected  to  a  head  of  water,  is  the  difficulty  of  filling  the 
intervals  between  wells  so  thoroughly  that  they  may  be  water- 
tight. The  filling  seldom  reaches  to  the  full  depth  of  the  wells, 
and  if  the  wells  should  have  sunk  out  of  plumb,  as  they  often 
do,  the  clearing  of  the  interspaces,  and  therefore  the  rendering 
of  them  water-tight,  becomes  almost  an  impossibility.  For 
this  reason  cast-iron  piling  with  grouted  joints  was  preferred 
to  a  line  of  wells  for  the  curtains  of  the  Assiout  and  Zifta 
barrages,  and  not  for  this  reason  only,  but  also  because  the 
piling  can  be  executed  expeditiously,  and  the  well-sinking 
cannot.  Time  is  required  to  construct  the  wells,  to  allow  for  the 
masonry  setting,  to  sink  the  wells,  and  to  close  the  intervals 
before  the  concrete  of  the  floor  can  be  commenced.  With 
cast-iron  piling  it  can  be  arranged  that  the  piles  shall  be  at  site 
before  the  excavation  is  ready  for  them,  and  that  they  shall  be 
driven  in  advance  of  the  final  clearing  of  the  foundation  bed, 
without  causing  any  delay  in  the  commencement  of  the  laying 
of  the  concrete. 

Wells  were  recently  used  in  Egypt  to  form  an  up-stream 
curtain  wall  to  a  new  head  built  to  the  canal  which  takes  off 
from  the  Nile  at  Cairo  and  flows  to  Ismailia,  carrying  the 
water  supply  of  Suez  and  Port  Said.  The  foundations  of  this 
work  were  as  treacherous  as  they  could  be,  and,  as  the  new 
work  was  to  replace  two  others  that  had  successively  failed,  it 
was  highly  desirable  that  there  should  not  be  a  third  failure. 
The  curtain  line  of  wells  was  sunk  5*75  metres  (19  feet)  below 
floor  surface,  or  canal  bed  level.  To  get  the  full  benefit  of  this 
depth  of  curtain,  it  was  necessary  to  arrange  for  a  water-tight 
closure  of  the  intervals  between  the  wells  to  their  full  depth. 
Piles,  made  of  half-inch  steel  plate  stiffened  with  T  irons,  were 
driven  outside  the  wells  to  close  the  intervals  (see  Fig.  46). 
These  piles,  though  flexible  to  a  certain  extent,  could  not  be 
expected  to  lie  so  close  against  the  masonry  of  the  wells  as  to 
produce  a  water-tight  joint.  So,  in  order  to  staunch  the  joints 
between  the  piles  and  the  wells,  a  pair  of  pipes  was  sunk  in  the 


,56 


IRRIGATION. 


well  intervals,  one  pipe  lying  in  each  of  the  angles  formed  by 
the  pile  and  the  faces  of  two  adjoining  wells.  The  length  of  pipe 
below  the  floor  foundation  level  was  perforated,  and  the  pipe 
was  so  placed  that  the  perforations  faced  the  angle  between 
pile  and  well.  The  pipes  were  sunk  by  means  of  a  jet  of  water 
playing  on  the  sand  at  the  foot  of  the  pipe  from  inside  the  pipe 

WELL  INTERVALS  SHUBRA 
FIG  46 


Tpp  '1-ijn.ij,  of 
Perforation* 


SECTION   ON    AB 


itself.  When  sunk  to  the  required  depth,  the  pipes  were  filled 
with  sand  to  ensure  the  exclusion  of  cement  grout  when 
grouting  the  floor.  In  that  operation  (which  will  be  described 
later)  the  cement  grout  encircling  the  pipes  made  a  water-tight 
joint  with  the  piles  and  wall  of  masonry  outside  the  piles,  so  that 
the  well  intervals  were  made  absolutely  water-tight  from  the 
bottom  to  the  top  of  the  grouted  floor,  above  which  it  was  of 


METHODS    OF  CONSTRUCTION.  157 

course  easy  tu  build  them  up  solid.  There  remained  the  depth 
of  interval  below  the  grouted  floor  to  render  water-tight.  After 
the  foundation  pit  had  been  laid  dry  by  pumping,  subsequent 
to  the  operation  of  grouting  the  floor,  the  staunching  pipes 
were  cleared  of  sand  by  means  of  a  jet  of  water,  and  were  then 
filled  with  grout  after  the  manner  of  grouting  up  the  joints  of 
the  cast-iron  piles  before  described.  It  was  found  in  every  case 
that  the  two  pipes  of  a  pair  were  in  communication  below  the 
grouted  platform  in  which  their  upper  ends  were  embedded,  as 
the  grout,  poured  down  one  pipe,  was  observed  to  rise  in  the 
other.  The  fact  observed,  namely,  that  these  pipes  were  in 
communication  with  each  other  under  the  grouted  floor,  makes 
it  almost  certain  that  the  arrangement  has  secured  a  continuous 
water-tight  curtain  wall  down  to  the  bottom  of  the  wells  along 
the  whole  of  the  up-stream  edge  of  the  floor. 

There  is  yet  another  method  of  getting  in  foundations  below 
water.  Cement,  used  in  the  form  of  grout,  for  binding 
together  materials  under  water,  had  been  used  successfully  in 
breakwaters  and  other  constructions  by  different  engineers 
before  the  system  received  its  most  notable  application  in  the 
construction  of  the  subsidiary  weirs  below  the  Delta  barrage  of 
Egypt.  In  discussing  this  method  it  will  be  convenient  to 
describe  first  the  practice  as  exemplified  in  the  building  of 
these  weirs,  and  to  state  afterwards  what  principles  must  be 
followed.  The  object  of  the  weirs  has  been  already  explained 
in  the  preceding  chapter,  and  the  design  is  given  in  Fig.  34. 
The  core  and  footing  walls  up  to  the  natural  level  of  the  water 
in  the  river  during  the  working  season,  and  also  the  foundation 
of  the  locks  associated  with  the  weirs,  were  formed  under  water 
by  the  cement  grout  system.  The  manner  of  proceeding 
was  as  follows  : — 

The  river  level  in  the  branch  selected  for  the  season's  work 
was  lowered  as  much  as  possible  by  shutting  down  the  gates  of 
the  Delta  barrage  up  stream  of  the  weir  site,  and  thus  diverting 
all  the  river  discharge  into  the  other  branch.  A  trench  was  then 


i58 


IRRIGATION. 


dredged  across  the  river  bed  to  dimensions  and  levels  corre- 
sponding with  the  foundation  bed  of  the  weir  and  its  lock,  as 
shown  on  the  designs  to  which  the  work  was  to  be  built. 
Along  this  trench  the  two  walls  of  the  weir  were  formed  of  a 
continuous  succession  of  blocks  from  one  side  of  the  river  to 
the  other  by  means  of  bottomless  boxes  put  together  in  the 
dredged  trench  with  the  help  of  floating  plant  (Fig.  47). 
The  boxes,  being  formed,  were  lined  with  sacking  by  the  help 

APPARATUS    FOR    FORMING 
GROUTED     BLOCK* 


Seaff 


FIG       47 


BARGE 


b.  Horizontal    Beams 
of   Box     Frames 


of  divers,  in  order  to  make  them  cement  grout-tight,  though  not 
water-tight.  Four  perforated  pipes  were  next  fixed  vertically 
at  equal  intervals  along  the  centre  of  the  box.  This  done,  the 
boxes  were  filled  up  to  a  little  above  water  level  with  rubble  of 
all  sizes  that  a  man  could  carry,  and  unperforated  pipes  were 
inserted  into  two  of  the  perforated  pipes,  reaching  almost  to  the 
bed  of  the  river  which  formed  the  bottom  of  the  box.  Funnels 
having  been  fixed  at  the  top  of  these  inner  pipes,  cement  grout 
was  poured  down  them.  Above  each  of  the  other  two  alternate 


METHODS  OF  CONSTRUCTION.  159 

pipes  was  arranged  a  stand  carrying  a  simple  grooved  wheel, 
over  which  a  string  ran,  having  at  one  extremity  a  ball  so 
weighted  that  it  sank  in  water  and  floated  in  the  cement  grout 
at  the  bottom  of  the  perforated  pipe,  and  at  the  other 
extremity  a  small  weight  just  heavy  enough  to  keep  the  string 
taut.  As  the  grout  rose  in  the  box  the  float  in  the  pipe  rose 
with  it,  and  the  small  weight,  moving  in  correspondence  down 
a  scale  fixed  to  the  stand,  registered  the  amount  of  rise.  When 
the  grout  had  risen  2  or  3  feet  the  inner  pipes  and  recording 
stands  changed  places,  and  grout  was  poured  down  the  second 
pair  of  pipes  till  the  gauges  over  the  other  pair  recorded  a 
further  rise  of  2  or  3  feet ;  whereupon  inner  pipes  and  recorders 
changed  places  again,  and  so  on  till  the  grout  had  mounted  to 
the  top  of  the  stones,  displacing  all  the  water  in  the  bcx.  As 
the  sea  of  grout  rose  from  below,  the  inner  pipes  were  gradually 
shortened  by  successively  unscrewing  the  short  lengths  of 
which  they  were  made  up.  The  object  of  this  was  that  the 
fresh  grout,  being  delivered  just  below  the  surface  of  the  rising 
grout,  might  not  disturb  the  lower  layers  and  interfere  with  the 
process  of  setting.  Cement  grout  is  twice  as  heavy  as  water ; 
consequently  the  grout,  if  delivered  below  the  water,  would 
remain  there,  and  would  displace  the  water  simply  by  its 
gradual  rise  from  below.  To  permit  of  the  ready  escape  of  the 
water,  vents  were  made  in  the  sides  of  the  boxes  just  above  the 
level  of  the  water  outside. 

If  the  cement  grout  had  been  poured  directly  into  the 
perforated  pipes,  each  bucket  of  grout  would  have  had  to  fall 
through  water,  and  have  at  least  suffered  in  quality,  if  it  had 
not  been  altogether  "  killed  "  by  excess  of  water.  By  using  an 
inner  unperforated  pipe,  with  its  lower  end  just  below  the  sur- 
face of  the  rising  sea  of  liquid  cement,  a  continuous  column  of 
grout  was  added  to  the  previous  mass  without  any  further 
admixture  of  water.  This  is  an  important  point  to  pay  atten- 
tion to  if  this  method  of  construction  is  imitated  elsewhere. 
Another  important  condition  is  that  the  grout  must  be  of  neat 


160  IRRIGATION. 

cement,  without  the  addition  of  sand  or  other  foreign  material . 
for  if  a  mixture  is  made  of  substances  of  different  specific 
gravities,  the  constituents  will,  in  the  liquid  form  of  grout, 
separate  from  each  other  under  the  action  of  gravity,  and  form 
distinct  strata  before  the  setting  properties  of  the  cement  have 
had  time  to  prevent  the  segregation. 

As  soon  as  the  cement  grout  had  risen  in  the  box  high 
enough  to  envelop  the  top  stones,  or  slightly  higher  than  the 
water  outside  the  box  in  the  river,  the  scum  was  cleared  off. 
small  stone  was  bedded  in  the  surface  grout,  and  the  box  and 
its  contents  left  alone  till  the  following  morning,  when  it  was 
found  that  the  block  had  set  sufficiently  to  stand  by  itself. 
The  parts  of  the  box  containing  it  were  then  cast  loose  and 
moved  forward  to  form  the  next  block,  and  so  on  across  the 
river.  Work  was  started  on  the  core  wall  foundations  at 
several  points  along  the  line  simultaneously  by  the  different 
rafts  fitted  up  for  the  purpose.  At  each  point  of  starting  the 
first  box  formed  was  four-sided.  On  the  completion  of  the 
first  block  one  end  of  the  box  was  removed,  and  the  next  and 
subsequent  boxes  were  made  with  the  three  remaining  sides, 
the  block  last  formed  closing  the  fourth  side.  The  upper  part 
of  the  core  wall  above  water  level  was  then  built  in  the  dry, 
and  the  clay,  rubble,  and  apron  blocks  put  in  place. 

Plate  VII.  shows  the  west  weir  under  construction.  The 
wall  on  the  left  is  the  lower  part  of  the  core  wall  which  was 
formed  by  grouting,  the  water  level  having  sunk  since  the  near 
blocks  were  made.  The  wall  on  the  right,  appearing  just  above 
water  level,  is  the  footing  wall.  The  near  cross-wall  is  a  con- 
necting wall  which,  in  its  finished  state,  will  form  a  toe  to 
support  the  shore  abutment  slopes;  the  farther  cross- wall,  of 
which  the  closing  block  is  being  formed,  is  the  first  of  four 
made  at  intervals  of  100  metres  to  divide  the  weir  into  compart- 
ments. Beyond  that  is  an  Interval  through  which  the  reduced 
discharge  of  the  river  is  allowed  to  pass.  On  the  far  side  of 
the  river  the  floating  plant  is  at  work  forming  the  blocks  of  the 


METHODS  OF  CONSTRUCTION.  l6l 

distant  lengths  of  the  two  walls,  which  will  later  on  be 
connected  across  the  central  channel  with  the  walls  on  the  near 
side.  The  depth  of  water  against  the  core  wall  at  the  time 
of  taking  the  photograph  was  20  feet,  and  against  the  footing 
wall  10  feet. 

The  dimensions  of  each  block  made  along  the  core  wall 
trench  were  10  metres  long  by  3  metres  broad  and  7J  to 

6  metres  high  (32  feet  9  inches  by  9  feet  10  inches  by  24  feet 

7  inches  to  19  feet  8  inches) ;  that  is,  each  block  was  about  half 
the  size  of  a  two-storeyed  cottage.     These  blocks  were  formed 
wholly  under  water. 

The  proportion  of  cement  to  the  quantity  of  masonry  formed 
by  this  method  is  37  per  cent.,  a  high  figure  for  concrete;  but 
the  rapidity  and  certainty  with  which  the  work  can  be  executed 
produce  economies  under  other  heads  of  expenditure,  and  the 
results  obtained  are  so  perfect  as  to  justify  the  employment  of 
this  system,  even  if  it  be  comparatively  costly,  wherever 
perfection  in  the  quality  of  the  work  and  rapidity  of  construction 
are  desired. 

As  the  method  of  cement  grouting  was  adopted  for  getting  in 
the  sub-aqueous  portions  of  the  weir  proper,  so  as  to  avoid  the 
difficulties  and  disadvantages  of  dealing  with  springs  which  are 
encountered  when  the  method  of  unwatering  the  foundations  is 
resorted  to,  it  seemed  desirable  and  consistent  to  apply  the 
same  method  to  the  lock  foundations,  an  undertaking  which 
had  never  been  attempted  before.  The  floor  surface  of  the 
finished  lock  would  be  below  the  low  water  level  of  the  river, 
so  that  the  grouting  of  the  foundation  could  not  be  continued 
till  the  grout  rose  to  water  surface,  as  in  the  case  of  the  core 
wall  blocks,  but  had  to  be  arrested  when  the  grout  had  risen  to 
a  level  2^  metres  (about  8  feet)  below  the  water  surface.-/  The 
manner  of  execution  was  as  follows  :  The  foundation  bed  was 
first  dredged  out  to  the  necessary  level,  which  was  4^  metres  (say 
15  feet)  below  low  water  level.  Two  parallel  walls  (see  Fig.  48), 
bounding  all  the  lock  area  on  either  side3  were  then  formed  by 

I.  M 


1 62 


IRRIGATION. 


the  same  system  as  that  adopted  for  the  foundations  of  the 
core  wall,  and  with  the  same  plant.  The  rectangle  of  which 
these  walls  formed  the  sides  (100  metres  by  17  metres,  or 
328  feet  by  56  feet,  in  the  clear  between  the  walls)  was  then 
closed  at  the  two  ends  by  sheet  piles  supported  by  horizontal 
beams  which  were  kept  in  place  by  pi'es  driven  a  short 

GROUTING    METHOD    OF 
GETTING    IN    FOUNDATIONS 
HALF  CROSS    SECTION  OF    LOCK 


FIQ      48 


4  INNER  PIPE 


SECTION   OF   ONE    END   WALL 


FIQ     49  . 


distance  into  the  bed  of  the  river  and  tied  at  their  tops  to  the 
side  walls  already  made  (see  Fig.  49).  A  staging  was  then 
constructed  across  the  enclosed  space  from  side  wall  to  side 
wall,  the  perforated  pipes  having  been  first  fixed  in  place  about 
3j  metres  (loj  feet)  apart  all  over  the  area.  The  pipes  were 
fitted  with  iron  brackets  to  make  them  serve  as  upright  sup- 
ports for  the  staging.  Two  metres  depth  of  rubble,  concrete 


METHODS  OF  CONSTRUCTION.  163 

metal  and  pebbles  were  then  thrown  in  to  form  the  floor 
foundation.  At  about  i  metre  distance  from  the  two  ends 
of  the  lock  area  a  second  interior  line  of  sheet  piling  had  been 
arranged  with  its  lower  end  below  the  level  to  which  the 
2-metre  layer  of  rubble  would  come  (Fig.  49).  All  the  sheet 
piling  was  lined  on  the  inside  with  sacking  to  prevent  the 
escape  of  cement  grout  between  the  joints,  in  the  same  way  as 
in  the  boxes.  When  the  2-metre  depth  of  floor  material  had 
been  deposited,  as  ascertained  by  sounding  rods,  grouting 
commenced  at  one  end  of  the  lock  and  continued  till  the 
other  end  was  reached,  the  level  to  which  the  grout  rose  being 
noted  by  the  float  and  gauge  arrangement  as  used  on  the  boxes. 
When  the  2-metre  layer  had  been  given  time  enough  to  set,  the  end 
spaces  were  filled  up  with  stone  and  grouted.  After  three  days' 
interval  the  enclosed  space  was  pumped  out,  and  the  grouting 
was  found  to  have  formed  a  perfectly  sound  floor  without  the 
sign  of  a  spring  in  it.  The  rest  of  the  lock  floor  and  walls  was 
built  in  the  dry  in  the  ordinary  way  after  clearing  and  cleaning 
the  surface  of  the  grouted  platform. 

The  advantages  of  this  system  of  cement  grouting  are  that 
the  springs  never  get  a  chance  of  troubling,  and  the  sub-aque- 
ous work  constructed  by  its  employment  is  perfect  in  quality 
and  of  a  strength  more  than  sufficient.  No  expensive  plant  is 
required  and  no  skilled  labour,  except  only  a  few  carpenters 
and  mechanics  to  prepare  the  parts  of  which  the  boxes  are 
formed,  and  a  few  intelligent  supervisors  to  direct  the  putting 
of  them  together.  The  system  has  also  the  merit  of  rapidity  of 
construction.  The  objection  to  it  is  its  costliness,  though  much 
of  the  expenditure  in  cement  is  balanced  by  economy  in  staff 
and  in  all  the  extra  outlay  which  accompanies  a  prolongation 
of  the  period  of  construction. 

The  use  of  cement  grout  for  the  construction  of  the  Delta 

barrage  weirs  was  preceded  by  a  remarkable  operation  on  the 

Delta  barrage  itself  carried  out  with  the  help  of  cement  grout, 

in  imitation    of   similar    work  done   some    years    previously 

M    2 


164  IRRIGATION. 

at  the  Hermitage  Breakwater,  Jersey,  by  the  late  Mr.  W.  R. 
Kinipple.  v  It  will  be  remembered  that  the  bottom  layer 
of  the  concrete  platform  on  which  the  barrage  rests  had  its 
cementing  material  washed  away  during  construction  by  springs, 
leaving  loose  concrete  metal  behind.  This  defective  layer,  and 
the  original  unsound  floor  above  it,  was  covered  over  and  cut  off 
from  communication  with  the  river  water  by  Colonel  Western's 
enveloping  additions  to  the  floor.  But  the  loose  material  still 
remained,  affording  a  passage  of  practically  no  resistance  to  the 
travel  of  the  percolation  water  along  that  length  of  its  path 
which  followed  the  under-side  of  the  original  foundations.  It 
was  felt  that,  if  this  bottom  stratum  of  the  old  floor  could 
be  made  impermeable,  additional  security  would  be  obtained. 
The  introduction  of  cement  grout  under  pressure  to  the  bottom 
layer,  with  the  view  of  filling  the  interstices  of  the  concrete 
metal  with  set  cement,  was  the  method  selected.  The  accom- 
panying diagrams  (Fig.  50)  will  help  to  make  the  following 
description  of  the  process  intelligible. 

Holes  were  first  bored  as  shown  by  the  strong  black  lines, 
and  cleared  to  at  least  i  metre  below  the  lowest  level  of  the 
foundations.  Cement  grout  was  then  poured  into  each  bore, 
and  the  pouring  continued  until  the  grout  filled  the  bore  to  the 
level  of  the  roadway  or  pier  tops.  When  the  bore  was  full,  the 
pressure  exerted  by  the  column  of  cement  at  the  bottom  of 
the  bore  was,  in  the  case  of  the  bores  made  from  roadway  level, 
26  tons  per  square  metre  (2*4  tons  per  square  foot),  and,  in  the 
case  of  the  two  others,  19  tons  per  square  metre  (176  tons  per 
square  foot).  So  great  a  pressure  was  sufficient  to  force  the 
cement  into  all  cavities  in  communication  with  the  bore,  so 
that  the  grout  must  first  have  enveloped  all  loose  material,  and 
then,  by  its  property  of  setting,  have  compacted  it  into  a  solid 
mass.  That  the  cement  did  not  fail  to  set  was  sufficiently 
proved,  as  in  several  instances  it  was  brought  up  in  a  hard 
state  when  clearing  the  adjacent  bore  to  which  it  had  travelled 
below  the  floor. 


METHODS  OF  CONSTRUCTION. 


165 


In  consequence  of  the  success  obtained  at  the  Delta  barrage, 
cement  grout  was  employed  to  overcome  difficulties  of  construc- 
tion in  other  troublesome  works  which  the  irrigation  officers  of 
Egypt  had  to  execute.  One  of  these  it  may  be  of  advantage  to 
instance  as  affording  an  example  of  the  combination  of  the  two 

DELTA    BARRAGE 
BORES    FOR  GROUTING 


CROSS     SECTION 


W.L. 


FIG     60 


PLAN 


ADWAY     OVER     BARRAGE 


systems  of  well-sinking  and  cement  grouting  for  getting  in 
foundations  below  water  level.  Reference  has  already  been 
made  to  the  Ismailia  Canal  head  when  describing  an  arrange- 
ment for  making  a  water-tight  closure  in  the  intervals  between 
wells.  On  account  of  the  treacherous  nature  of  the  subsoil 
which  would  have  to  bear  the  weight  of  the  work,  it  was 
decided  to  sink  wells  below  the  general  floor  foundation  level, 


166  IRRIGATION. 

with  the  object  of  giving  increased  support  to  the  lock  and 
abutment  walls  and  of  providing  curtain  walls  up  stream 
and  down  stream.  By  the  addition  of  a  few  wells  elsewhere  a 
continuous  boundary  of  wells  was  formed  enclosing  the  whole 
foundation  area.  These  were  sunk  to  the  required  depth,  their 
tops  being  then  at  about  the  level  of  the  future  floor  surface.  To 
execute  the  well-sinking,  as  well  as  the  necessary  preliminary 
excavations,  a  bank  had  to  be  formed  on  the  Nile  side  to  keep 
out  the  river  water,  and  pumps  had  to  be  constantly  at  work  to 
keep  the  inside  water  down.  The  excavation  of  the  foundation 
pit  was  carried  down  by  hand  as  low  as  possible,  which  was  to  a 
level  some  2  metres  (6  feet)  short  of  floor  foundation  level.  As  at 
this  level  strong  springs  rose  over  the  whole  area  of  the  founda- 
tions through  black  sand  in  a  formidable  manner,  and  as 
previous  experience  had  shown  how  difficult  it  was  to  build 
sound  work  on  such  a  substratum  of  quicksand  with  springs 
rising  through  it  everywhere,  it  was  decided  to  get  in  the  floor 
platform  all  over  the  area  bounded  by  the  wells  by  the  cement- 
grouting  method,  as  was  done  in  the  construction  of  the  weir  locks 
of  the  Delta  barrage.  The  programme  which  was  followed  was 
this :  After  closing  the  intervals  between  the  wells  by  iron  piles, 
the  "saddle-back  "  and  rubble  pitching  up  stream  of  the  regulator 
and  lock  were  completed  to  the  extent  shown  in  Fig.  46.  The 
wing  walls  were  built  up  over  their  wells  to  a  considerable 
height  above  the  finished  level  of  the  floor.  The  river  dam  was 
then  cut,  and  the  water  allowed  to  rise  in  the  pit  and  find  its 
own  level.  A  sand  dredger  was  next  admitted  through  the 
opening  in  the  dam,  and  the  foundations  of  the  floor  were 
dredged  out  to  full  depth.  The  dredger  having  done  its  work 
made  its  exit,  and  the  cut  in  the  dam  was  closed  again.  The 
grouting  pipes  and  staging  were  then  arranged  over  the  founda- 
tion area.  As  soon  as  the  pipes  were  in  place  rubble  was 
thrown  in  round  them  to  the  required  height  of  nearly  2  metres 
(about  6  feet).  Grouting  was  then  carried  on  after  the  manner 
already  described,  and  continued  till  the  floor  rubble  was  grouted 


METHODS  OF   CONSTRUCTION.  16; 

to  the  top.  The  work  was  left  undisturbed  for  three  days,  after 
which  the  pumps  were  set  to  work  to  lower  the  water  in  the 
enclosed  foundation-  pit.  When  the  surface  of  the  grouted 
platform  had  been  laid  dry  and  cleaned,  it  was  found  that  the 
operation  had  been  successful,  and  that  there  were  no  springs 
left  to  interfere  with  the  work.  The  floor  was  then  completed 
and  the  superstructure  built  in  the  dry. 

It  is  sometimes  desired  to  lay  a  syphon  under  a  running 
canal  which  cannot  be  closed  for  a  period  sufficiently  long  to 
allow  of  its  construction  in  the  ordinary  manner.  The  usual 
method  would  be  to  divert  the  canal  into  a  temporary  channel 
passing  outside  the  syphon  site.  But  there  are  some  situations 
where  a  diversion  cannot  be  made  except  at  a  prohibitive  cost. 
In  such  cases  some  method  of  laying  the  syphon  under  water 
must  be  devised.  In  Egypt  several  pipe  syphons  of  5  feet 
diameter,  some  of  them  over  250  feet  in  length,  have  been  laid 
in  running  canals  without  resorting  to  the  usual  method  of  a 
diversion.  The  barrel  of  the  syphon  may  consist  of  a  pipe  of  five- 
sixteenths  to  half  an  inch  thickness  of  mild  steel  plate,  stiffened 
with  angle  irons  and  cover  plates.  The  pipe  is  put  together  on 
the  canal  bank  in  the  neighbourhood  of  the  syphon  site.  The  two 
ends  of  the  pipe  are  closed  with  water-tight  doors,  and  means  of 
admitting  water  provided.  The  pipe  is  then  launched  and 
floated  into  correct  position  over  a  trench  which  has  been 
dredged  out  across  the  canal  ready  to  receive  it.  Temporary 
banks,  made  round  the  outer  ends  of  the  dredged  trench,  connect 
the  extremities  of  the  canal  banks  which  have  been  cut  through 
to  form  the  trench  for  the  pipe.  The  pipe  is  now  ready  for 
sinking.  It  is  dangerous  to  let  the  water  into  it  and  leave  it 
to  find  its  own  way  to  the  bottom.  It  would  certainly  tilt  in 
doing  so,  one  end  sinking  and  the  other  rising  up  out  of  the 
water,  and  the  joints  would  be  so  strained  that  a  leak  would 
probably  be  the  result.  To  control  the  sinking,  the  pipe  should 
be  supported  at  both  ends  by  ropes  manipulated  from  rafts  or 
boats,  and  the  ropes  should  be  paid  out  evenly,  so  that  the  pipe 


168  IRRIGATION. 

may  be  let  down  quietly  in  a  horizontal  position  on  to  its  bed. 
When  the  pipe  is  in  place,  the  canal  banks  are  remade  over  it 
in  their  former  alignment,  and  the  ends  of  the  syphon  outside 
the  canal  banks  completed. 

The  building  of  the  masonry  ends,  or  the  fixing  on  of  the 
rising  terminal  pipes,  is  sometimes  a  matter  of  considerable 
difficulty  on  account  of  the  proximity  of  the  flowing  canal.  In 
the  case  of  a  syphon  of  two  pipes  of  5  feet  diameter  laid,  by  the 
system  just  described,  under  the  Ibrahimia  Canal,  in  Upper 
Egypt,  the  ends  were  formed  of  bent  continuations  of  the 
horizontal  pipes  rising  to  the  inlet  and  outlet  levels  at  either 
end.  After  the  horizontal  lengths  had  been  successfully  got 
into  position  and  the  canal  banks  remade  over  them,  it  was 
found  impossible  to  get  rid  of  the  water  about  the  pipe  ends  so 
as  to  admit  of  the  rising  lengths  being  added.  So  the  horizontal 
lengths  were  lifted  again,  the  bends  and  part  of  the  rising  ends 
added  above  water,  and  the  sinking  repeated.  In  this  way  the 
work  was  successfully  completed. 

The  same  difficulty  of  building  the  ends  of  another  syphon 
in  Egypt  was  surmounted  in  quite  a  different  way.  The  syphon 
was  a  simple  pipe  of  5  feet  diameter  with  masonry  inlet  and 
outlet  wells  at  its  extremities.  The  pipe  was  got  into  place 
successfully,  but  the  endeavour  to  complete  it  by  building 
the  masonry  ends  outside  the  banks  was  for  a  long  time 
abortive,  on  account  of  the  high  level  water  in  the  canal 
close  alongside  and  the  moving  sand  below.  Eventually  a 
masonry  well  was  sunk  as  near  the  end  of  the  pipe  as 
possible  (Fig.  51),  but  there  remained  an  interval  of  6  to  8 
inches  between  the  two.  The  pipe  end  was  closed  by  a 
wooden  door  and  tarred  canvas,  kept  pressed  against  the  pipe 
by  wedges  driven  by  divers  between  door  and  well.  A  crater 
was  then  dredged  out  with  its  bottom  from  18  inches  to  2  feet 
below  the  under-side  of  the  pipe.  An  upright  grouting  pipe, 
perforated  at  its  lower  end,  was  fixed  as  shown  in  Fig.  51. 
Rubble  was  then  deposited  at  the  bottom  of  the  crater  up  to  a 


METHODS  OF  CONSTRUCTION. 


I69 


third  of  the  pipe's  diameter,  and  the  mass  grouted  up.  A  box 
was  then  formed  on  the  top  of  the  grouted  block  with  the  well- 
face  as  one  side  of  it,  and  the  box  was  filled  with  rubble  to  a 
height  of  2  feet  over  the  pipe.  The  contents  of  the  box  were 
then  grouted  up  to  the  top.  After  a  couple  of  days  the  water 
in  the  well  was  pumped  out,  and  a  passage  cut  between  the 
well  and  pipe  to  the  same  diameter  as  the  pipe  and  in  prolonga- 
tion of  it.  The  collar  of  grouted  rubble  was  found  to  have 
formed  a  perfectly  water-tight  joint  between  the  well  and  the 
pipe.  Both  ends  of  the  syphon  were  treated  in  the  same  way. 


END    OF    PIPE-SYPHON 


w.i. 


FIG    5t 


PIPE    PASSING  "N^ 

UNDER    CANAL      ' 


The  well  walls  were  then  cut  down  on  the  outside  to  the  proper 
levels  for  the  sills,  and  the  slope  revetments  completed. 

The  tunnel  which  was  designed  to  carry  a  double  line  of  rail- 
way under  the  Detro/t  river,  between  Windsor  on  the  Canadian 
side  and  Detroit  on  the  United  States  side,  was  constructed  on 
somewhat  the  same  system  as  the  syphon  just  described.  The 
tubes  were  floated  into  place  and  sunk  into  a  trench  dredged 
out  to  receive  them.  But  the  tunnel  was  made  up  of  several 
tube  lengths  which  had  to  be  fastened  together  under  water. 
The  manner  of  caulking  the  joints  between  two  adjacent  lengths 
was  thus  described  in  the  Standard  of  November  ist,  1906.  The 


170  IRRIGATION. 

passage  is  quoted  here  as  the  device  may  be  found  useful  in  the 
construction  of  irrigation  syphons.  "  Each  tube  when  manu- 
factured will  be  fitted  with  a  sleeve  at  one  end,  which  can  slip 
over  the  end  of  the  adjoining  tube  previously  sunk.  The  sleeve 
is  to  be  provided  with  a  flange  which  can  be  bolted  to  a  coi  re- 
sponding flange  of  the  adjoining  tube,  a  rubber  gasket  being 
placed  between  the  two.  A  similar  rubber  gasket  is  to  be  pro- 
vided at  the  inner  end  of  the  sleeve,  bearing  up  against  the  edge, 
of  the  next  tube.  In  bolting  up  the  flanges,  which  must  be 
done  by  divers,  the  rubber  gaskets  must  be  squeezed  together 
between  the  ends  of  the  tubes  to  form  a  tight  joint.  This  space 
will  be  filled  with  a  grout  of  pure  cement.  The  ends  of  the 
tubes  at  the  joints  are,  further,  to  be  fitted  with  flange  angles 
on  the  inside  for  the  purpose  of  caulking  between  them  should 
the  joints  be  found  to  leak.  In  order  to  enable  the  contractors 
to  begin  lining  the  tubes  before  the  sections  are  sunk  all  the 
way  across  the  river,  some  of  the  tubes  may  be  provided  with 
bulkheads  to  keep  out  the  water  when  the  tubes  laid  are  being 
pumped  out." 

The  work  was  begun  in  1906  and  finished  in  1910.  It  will 
be  found  described  in  a  paper  by  W.  J.  Wilgus,  No.  3915, 
Detroit  River  Tunnel :  Minutes  of  Proceedings  of  the  Institution 
of  Civil  Engineers,  1911. 


CHAPTER  VIII. 

MEANS  OF   DISTRIBUTION. 

Canals  and  Drains. 

IN  Chapter  VI.  the  means  of  drawing  water  from  the  source 
of  supply  were  considered.  In  this  chapter  a  description  will 
be  given  of  the  means  by  which  the  water  is  carried  from  the 
source  and  distributed  to  the  fields  on  which  artificially  irrigated 
crops  are  to  be  raised. 

A  canal  system  consists  of  channels  to  carry  the  water,  of 
regulating  works  (usually  of  masonry)  to  control  its  flow,  and 
of  drains  to  discharge  surplus  water  from  the  irrigation  zone. 

The  irrigation  channels  are  usually  classified  under  the  heads 
of  main  canals,  branch  canals,  distributaries,  and  field  channels. 
Assuming  that  the  position  of  the  offtake  has  been  selected, 
the  main  canal,  between  its  head  and  the  point  where  it  first 
enters  the  tract  to  be  irrigated,  should  be  carried  along  the 
alignment  which  is  economically  the  most  advantageous.  The 
shorter  this  unprofitable  length  of  canal  can  be  made  the 
better,  provided  that  the  selection  of  a  favourable  site  for  the 
head  works  is  not  unduly  influenced  by  the  claims  of  economy 
to  the  neglect  of  more  important  considerations.  Within  the 
area  commanded — that  is,  inside  the  limits  of  the  land  which 
is  to  be  brought  under  irrigation — the  alignment  of  the  canals 
must  be  such  as  to  facilitate  direct  irrigation  from  them.  It 
the  country  is  made  up  of  ridges  and  intervening  depressions, 
the  main  canal  should  run  along  the  principal  ridge.  Its 
branch  canals  should  follow  the  subsidiary  ridges,  and  the 
distributaries  the  minor  ridges,  so  as  always  to  keep  the  water 
at  a  height  which  will  command  the  land  to  be  irrigated  and 


IRRIGATION. 

in  a  position  to  flow  on  to  the  fields,  and  also  to  avoid  crossing 
the  natural  drainage  lines  of  the  country.  If  a  contoured  map 
exists,  it  is  more  or  less  a  simple  matter  to  lay  down  upon  it 
the  scheme  of  canals  and  drains  adapted  to  the  natural  con- 
figuration of  the  ground.  But  the  configuration  may  not  be 
one  of  alternating  ridges  and  depressions.  There  is  need 
sometimes  of  designing  irrigation  systems  to  serve  the  flat 
lands  which  are  found  bordering  a  river  that  flows  along  a 
valley.  If  the  river  follows  the  lowest  line  of  the  valley  bed, 
these  plains  have  a  surface  slope  towards  it ;  but  if  the  river 
occupies  a  broad  valley  and  has  raised  the  land  level  alongside 
it  by  the  deposit  of  successive  floods,  the  land  surface  slope 
falls  away  from  the  river,  as  with  the  Nile  valley  in  Upper 
Egypt.  In  the  former  case  the  canal  would  be  aligned  along 
the  outer  edge  of  the  flat  tract  at  the  foot  of  the  rising  ground 
enclosing  the  valley,  and  in  the  latter  case  along  the  high 
margin  adjoining  the  river.  The  flat  lands  (vegas)  of  Anda- 
lucia,  in  Spain,  bordering  the  river  Guadalquivir,  may  be 
taken  as  an  example  of  lands  sloping  towards  the  river.  A 
canal  to  irrigate  them  would  have  to  be  aligned  along  the  foot 
of  the  hills  that  bound  the  valley,  and  would  unavoidably  cross 
all  the  drainage  lines  leading  to  the  river.  At  every  crossing 
a  passage  for  the  drainage  water  would  have  to  be  provided. 

But,  whatever  may  be  the  nature  of  the  country  through 
which  canals  are  carried,  no  attempt  must  be  made  to  prevent 
the  drainage  from  flowing  along  the  line  to  which  it  has 
established  a  "right  of  way,"  if  provision  can  be  made  for 
its  unimpeded  passage  by  constructing  either  a  syphon  to 
carry  it  under  the  canal  at  the  point  of  crossing,  or  some 
other  work  serving  the  same  end.  It  may,  however,  in  some 
cases,  be  preferable  to  divert  the  drainage  and  carry  it  away 
in  a  new  channel  made  expressly  for  it.  But,  in  any  case, 
the  universal  rule  applies  that  the  drainage  must  not  be 
ignored,  and  full  provision  must  be  made  for  the  disposal  of 
all  excess  water,  whether  it  be  due  to  rainfall  or  irrigation. 


MEANS  OF   DISTRIBUTION.  173 

The  principles  that  govern  the  alignment  of  drains  are  the 
converse  of  those  applicable  to  canals.  If  natural  drainage 
channels  do  not  already  exist  where  drainage  is  a  necessity, 
artificial  drains  must  be  aligned  along  the  lowest  lying  land, 
that  is,  along  the  bottom  of  the  depressions  or  valleys  between 
the  ridges  on  which  the  canals  and  distributaries  run. 

The  next  things  to  consider  are  the  points  which  influence 
the  design  as  regards  the  longitudinal  section  of  the  irrigation 
and  drainage  channels.  The  most  important  matter  affecting 
the  question  of  the  gradient  of  main  canals  is  silt  deposit. 
Silt  is  the  eroded  matter  which  is  brought  down  in  suspension 
by  rivers  from  their  upper  reaches.  The  greater  the  velocity  the 
more  and  the  heavier  is  the  silt  that  the  water  carries  along 
with  it.  When  the  river  leaves  the  hills  and  ceases  to  be 
torrential,  it  drops  its  heaviest  loads  of  shingle  and  boulders, 
but  keeps  the  sand  and  soft  mud  for  distribution  in  the  plains. 
Before  the  river  nears  the  sea  it  has  left  behind  all  but  the 
finest  sand  and  mud  which  give  the  richest  deposit  of  all. 
There  is  silt  which  is  fertilising,  and  there  is  silt  which  is  sterile. 
The  former  it  is  desirable  to  draw  into  the  canals  and  carry 
forward  to  the  fields  in  abundance ;  the  latter  it  is  better  to 
exclude  from  the  canals  altogether,  if  possible,  as  being  so 
much  "dead  weight  in  the  boat."  At  the  same  time,  it  is 
important  that  the  deposit  of  silt  in  the  canal  itself  should  be 
a  minimum.  As  silt  deposit  takes  place  wherever  there  is  a 
change  of  velocity  from  a  higher  to  a  lower  rate,  the  velocity 
of  flow  in  the  canal  which  ensures  the  transport  of  a  maximum 
amount  of  silt  to  the  fields  with  a  minimum  of  deposit  on  the 
way,  should  theoretically  be  the  same  as  that  of  the  river  at  the 
point  where  the  canal  takes  off  from  it.  ^  But  it  is  rarely,  if 
ever,  possible  to  carry  this  theory  into  practice,  for  not  only 
does  the  river  velocity  vary  at  different  seasons,  but  it  is 
sometimes  so  high  that,  if  the  canal  were  to  flow  at  the  same 
rate,  its  water  surface  slope  would  be  steeper  than  the  slope 
of  the  country,  and  the  water  would  never  come  to  land 


1/4  IRRIGATION. 

surface.  Consequently  it  is  found  more  practicable  to  make 
the  rate  of  river-flow  past  the  offtake  approximate  to  that 
of  the  canal  than  to  make  the  canal  agree  with  the  river. 
This  is  brought  about  by  working  the  gates  of  the  under- 
sluices  in  the  river  weir  or  regulator,  and  the  shutters  of  the 
canal  head,  in  such  a  way  as  to  discourage  as  far  as  possible 
strong  currents  and  eddies  in  the  neighbourhood  of  the  head 
sluice,  and  to  produce  comparatively  still  water  at  the  canal 
offtake.  The  coarser  and  heavier  silt  is  carried  along  by  the 
lower  water  in  contact  with  the  bed  of  the  river,  and  it  is 
this  material  that  it  is  desirable  to  exclude  from  the  canal, 
for  these  two  reasons,  namely,  that,  if  admitted,  it  is  sure  to 
cause  troublesome  deposit  in  the  first  reaches  of  the  canal ; 
and,  even  supposing  some  of  it  succeeded  in  reaching  the 
fields,  it  would  not  be  welcomed  there,  for  it  would  have  taken 
the  place  of  the  lighter  and  more  fertilising  silt  which  is  so 
valuable  to  farmers.  To  prevent  the  admission  of  this  heavy 
and  infertile  matter,  it  is  necessary  to  draw  in  the  upper  water 
from  the  river  and  to  exclude  the  lower.  This  is  sometimes 
effected  by  giving  the  canal  a  head  sluice  of  considerable 
length  and  a  raised  sill,  and  by  working  the  shutters  in  such 
a  way  that  the  top  layer  only  of  the  river  water  may  be  drawn 
into  the  canal.  But  this  method  of  drawing  off  from  the  river, 
and  of  reducing  the  rate  of  flow  past  the  canal  head  by  closing 
the  adjacent  under-sluices,  will  cause  some  of  the  excluded 
silt  to  be  deposited  in  front  of  the  head  sluice  and  above  the 
under-sluices.  This  must  be  got  rid  of  by  periodically  opening 
the  under-sluices,  so  as  to  create  a  sufficiently  high  velocity  to 
scour  away  the  deposit.  While  this  operation  is  being  carried 
out,  the  canal  head  should  be  temporarily  closed.  In  this  way, 
by  an  intelligent  management  of  the  regulating  gates  of  the 
under-sluices  and  of  the  canal  head,  the  silt  difficulty,  which 
has  troubled  every  irrigation  engineer,  may  be  at  least  partially 
overcome.  The  head  sluice  must  therefore  be  so  designed  that 
water  may  be  admitted  to  the  canal  in  accordance  with  these 


MEANS  OF   DISTRIBUTION.  175 

principles,  which  have  been   deduced  from   the   teachings   of 
experience,  chiefly  in  India  (Buckley,  Chapter  III.). 

It  is  not,  then,  the  river  velocity  that  determines  the  velocity 
of  flow  that  is  to  be  adopted  for  the  canal,  but  other  considera- 
tions. If  the  canal  is  to  be  navigable,  it  is  desirable  that  the 
velocity  should  be  as  low  as  is  consistent  with  its  more 
important  duty  of  irrigation,  the  avoidance  of  silt  deposit,  and 
a  reasonable  regard  for  economy  The  lower  the  velocity  of 
flow  the  larger  the  cross-section  must  be  to  carry  the  required 
discharge,  and  consequently  the  greater  the  cost  of  making  the 
canal.  If  the  velocity  is  too  low,  silt  deposits  in  the  canal, 
the  discharging  capacity  of  the  canal  is  diminished,  and  much 
expense  is  incurred  in  clearing  out  the  deposit.  If  the  velocity 
is  too  great,  the  reverse  takes  place ;  the  bed  is  scoured  out,  the 
banks  are  undermined  and  slide  forward,  and  the  channel  soon 
becomes  irregular.  Neglecting  the  needs  of  navigation,  the 
ideal  velocity  is  that  which  will  neither  create  scour  nor 
encourage  deposit,  but  will  enable  the  water  to  carry  forward 
the  silt  which  comes  into  the  canal  from  the  river,  and  keep  it 
in  suspension  until  the  field,  which  is  to  be  irrigated,  is  finally 
reached.  There  both  the  water  and  its  silt  will  find  useful 
work  to  do.  What  this  ideal  velocity  should  be  varies  with 
the  quality  and  quantity  of  the  silt  that  the  river  carries  in 
suspension,  and  with  the  nature  of  the  soil  forming  the  bed 
and  banks  of  the  canal. 

In  India  Mr.  R.  G.  Kennedy  has  attempted  to  determine  this 
point.  He  selected  for  his  observations  certain  canals  in  which 
the  flowing  water  carried  a  constant  percentage  of  silt  in 
suspension.  The  cross-sections  and  velocities  at  thirty  sites, 
where  no  silting  or  scouring  took  place,  were  measured,  and  it 
was  found  that  at  all  these  sites  the  following  equation 
expressed  very  approximately  the  invariable  relation  between 
the  mean  velocity  and  the  depth  of  the  water : — 
V  =  c  dm  =  0-84  d°'64 

Thus  the  higher  the  velocity  the  greater  would  be  the  correct 


176  IRRIGATION. 

depth,  and  vice  versa.  Therefore  it  follows  that,  for  a  given 
discharge,  canals  with  a  high  velocity  should  be  comparatively 
narrow  and  deep,  and  those  with  a  low  velocity  wide  and 
shallow.  On  different  canal  systems  the  values  of  c  and  m  in 
the  above  formula  might  be  expected  to  vary  slightly.  It 
would  appear  that  Mr.  Kennedy's  conclusions  require  further 
testing  before  they  can  be  confidently  accepted  as  the  expression 
of  prevailing  law.1 

It  is  chiefly  the  flood  conditions  that  have  to  be  taken  into 
account  in  determining  the  figure  to  adopt  for  the  velocity  of 
flow  in  the  canal.  During  the  season  of  low  discharge  the 
river  carries  little  or  no  silt ;  in  flood  it  is  carrying  its  maximum. 
In  Indian  rivers  during  flood,  the  proportion  by  weight  of  solid 
matter  to  liquid  may  be  as  great  as  I  to  30,  It  frequently 
happens  that  the  conditions  are  such  that  silt  is  deposited  in 
the  canals  during  flood,  and  picked  up  and  carried  away  by  the 
clearer  water  that  enters  after  flood,  even  though  the  velocity 
in  the  latter  case  may  be  lower.  This  is  due  to  the  fact  that, 
in  flood,  the  water  admitted  brings  in  more  silt  from  the  river 
than  the  canal  velocity  enables  the  water  to  keep  in  suspension  ; 
whereas,  after  the  flood,  the  clearer  water  is  not  carrying  all  it 
can,  and  so  picks  up  some  of  the  lighter  silt  as  it  goes  along. 
Mr.  Buckley  instances  the  case  of  the  Sirhind  Canal  in  India, 
on  which  careful  observations  of  silt  deposit  have  been  made. 
In  August  and  September  the  velocities  observed  were  3*2  and 
3*0  feet  per  second  respectively,  and  with  these  velocities  silt 
was  deposited :  in  October  and  November  the  velocities  were 
3*5  and  3*3  feet,  and  the  quantity  of  silt  that  was  removed  in 
these  two  months  was  more  than  double  the  quantity  that 
had  been  deposited  in  the  two  preceding  months.  In  the 
two  later  months,  when  scouring  replaced  deposition  of  silt, 
the  velocity  of  current  was  only  slightly  increased,  but  the 
flowing  water  was  clearer.  From  experiments  made  during 
the  flood  season  in  Lower  Egypt,  Sir  William  Willcocks  came 
to  the  conclusion  that,  in  canals  with  their  heads  suitably 

1  See  Note  8,  Appendix  IV. 


MEANS  OF  DISTRIBUTION.  177 

placed,  a  mean  velocity  of  from  70  to  roo  metre  (2*30  to  3*28 
feet)  per  second  is  sufficient  to  prevent  any  appreciable  deposit, 
but  that  deposit  takes  place  with  mean  velocities  of  '60  metre 
(2  feet)  a  second  and  under.  In  Lower  Egypt  the  silt  carried 
by  the  river  is  very  fine. 

It  may  be  stated,  as  a  conclusion  based  on  experience  in 
India  and  Egypt,  that  a  velocity  of  from  2  to  3  feet  a  second  is 
required  to  carry  forward  ordinary  silt,  the  required  velocity 
being  greater  or  less  according  as  the  matter  in  suspension  is 
coarse  or  fine,  and  the  water  heavily  or  lightly  charged  with 
silt. 

The  velocity  of  flow  depends  on  the  surface  slope  of  the 
water  in  the  canal.  In  the  first  reach  of  the  main  canal, 
between  its  head  and  the  upper  limit  of  the  land  commanded 
by  the  canal  water,  the  water  surface  slope  must  be  steep 
enough  to  produce  a  velocity  that  will  decidedly  discourage  silt 
deposit.  But,  provided  this  condition  is  fulfilled,  it  is  advan- 
tageous to  have  a  surface  slope  of  low  gradient,  as  the  flatter 
the  slope  is,  the  shorter  will  be  the  length  of  canal  required  to 
bring  the  water  to  country  surface.  Within  the  commanded 
area  the  surface  slope  of  the  canal  is  determined,  in  most 
cases,  by  the  slope  of  the  land.  If,  however,  the  land  surface 
is  so  steep  that  a  water  surface  slope  which  conforms  to  it 
gives  an  inconveniently  high  velocity  in  the  canal,  the  canal 
must  be  divided  up  into  reaches  with  a  suitable  gradient, 
produced  by  impounding  the  water  at  regulating  falls  situated 
at  the  lower  end  of  each  reach. 

The  velocity  of  flow  and  water  surface  slope  having  been 
determined  from  the  foregoing  considerations,  there  remains  to 
be  calculated  the  discharge  the  canals  will  have  to  carry.  The 
data  for  this  calculation  are  the  area  of  crop  to  be  irrigated 
and  the  accepted  "  duty  "  of  water  for  the  period  of  maximum 
demand.  In  India  the  kharif  season  and  in  Egypt  the 
flood  season  are  the  periods  in  which  the  canals  have,  in  most 
cases,  to  carry  the  greatest  discharges.  Mr.  Buckley  states 


178  IRRIGATION. 

that,  "  as  a  general  rule,  main  canals  irrigating  khareef  (or 
monsoon)  crops  should  be  capable  of  carrying  a  maximum 
discharge  of  I  cubic  foot  per  second  for  every  fifty  acres  of  that 
crop  which  it  is  intended  to  irrigate,  and  they  should  be  capable 
of  carrying  I  cubic  foot  for  each  100  acres  of  rabi  (cold  weather) 
crops.  The  extent  of  land  which  can  be  irrigated  may  be 
determined  either  by  the  quantity  of  water  available  in  the 
source  of  supply  or,  when  the  quantity  is  abundant,  by  the 
area  which  can  be  commanded  by  the  system." 

In  Egypt,  during  the  Nile  flood,  the  supply  is  abundant 
and  sufficient  for  the  area  commanded.  The  whole  of 
the  perennially  irrigated  tracts  are  commanded  by  the  canal 
systems  of  Egypt,  and  so  the  area  commanded  becomes 
identical  with  the  gross  area.  The  discharge  which  the 
canals  have  to  carry  in  flood  to  serve  this  area  is  calculated 
at  the  rate  of  25  cubic  metres  a  day  per  acre.  This  is  equivalent 
to  an  allowance  of  i  cubic  foot  a  second  for  every  ninety-eight 
acres.  The  area  under  rice  in  Egypt  is  insignificant  as  compared 
with  the  total  area  under  irrigation  during  the  flood  season  ; 
otherwise  it  would  have  to  be  separately  allowed  for  in  the 
estimate  at  double  the  general  rate.  Nevertheless  it  is  as  well  to 
add  a  small  percentage  to  the  total  to  provide  for  the  rice  crop, 
and  also  for  the  washing  of  salted  lands  which  is  carried  on  when 
water  is  plentiful.  The  allowance  in  Egypt  may  therefore  be 
taken  to  be  rather  more  than  the  rabi  allowance  of  India  of  i 
cubic  foot  a  second  for  every  100  acres. 

The  velocity  of  flow  and  the  maximum  discharge  are  the 
factors  with  which  the  calculations  of  the  dimensions  of  a 
canal  are  made.  Its  cross-section  must  come  under  considera- 
tion at  this  stage.  A  theoretically  perfect  cross-section  for 
a  large  canal  demands  a  depth  that  would  be  found  unsuitable 
for  several  reasons.  Not  only  would  the  original  excavation  of 
the  canal  in  deep  cutting  be  difficult  and  costly,  but  the  sub- 
sequent maintenance  of  a  clear  channel  to  full  depth  by 
dredging  or  otherwise  would  be  troublesome.  It  can  be  readily 


MEANS  OF  DISTRIBUTION. 


179 


understood  that  the  cost  and  difficulty  of  excavation  becomes 
very  great  as  soon  as  spring  level  is  reached.  The  depth  of 
large  canals  is,  therefore,  made  as  great  as  may  be  found  con- 
venient under  the  conditions  affecting  the  question.  The  width 
that  will  give  a  channel  of  the  required  discharging  capacity  is 
then  found  by  the  help  of  hydraulic  tables.1 

As  examples  of  the  head  reaches  of  canals  in  cutting,  two 
sections  are  given  (Fig.  52).  The  upper  one  is  typical  of  Indian 
canals ;  the  lower  is  that  of  a  recently  made  canal  in  Egypt. 
In  India,  where  rain  falls  heavily,  it  is  necessary  to  make  a 


MAIN    CANALS    IN    CUTTING 


PIG  52 


SECTION 
CANAL       ABBAS 


system  of  drains  on  the  inside  berms  to  prevent  the  slopes 
being  worn  into  gutters.  In  Egypt  the  rainfall  is  so  light  that 
this  precaution  is  unnecessary. 

Main  canals  are  run  with  a  constant  supply,  and  with  a  water 
surface  not  necessarily  above  country  level.  It  is,  in  fact, 
desirable  to  keep  the  water  level  as  low  as  possible,  consistently 
with  a  delivery  at  convenient  levels  to  branch  canals,  for 
several  reasons.  Direct  irrigation  from  a  main  canal  should 
be  discouraged  as  much  as  possible  on  account  of  the  difficulty 
of  effecting  a  fair  distribution  of  a  limited  supply  of  water  by 

1  Jackson's  "  Canal  and  Culvert  Tables,"  Higham's  "  Hydraulic  Tables," 
and  Colonel  Moore's «'  New  Tables,"  will  be  found  useful.  See  Appendix  II. 


180  IRRIGATION. 

any  system  of  rotations  when  such  a  practice  is  allowed.  More- 
over, as  main  canals  flow  with  a  water  surface  at  a  constant 
level  for  long  periods,  it  is  best  to  keep  the  water  within  soil  to 
avoid  the  evils  of  infiltration  and  consequent  waterlogging 
of  the  soil  outside  the  canal.  To  provide  for  the  irriga- 
tion of  the  land  adjoining  a  main  canal,  parallel  high  level 
distributaries  should  run  alongside  to  take  up  the  direct 
irrigation. 

It  is  not  possible  to  define  in  terms  that  are  universally 
applicable  a  main  canal,  a  branch  canal,  and  a  distributary. 
It  is  not  always  easy  to  decide  where  a  main  canal  becomes  a 
branch  canal,  or  where  a  branch  canal  becomes  a  distributary. 
A  branch  canal  is  at  any  rate  intermediate  in  position  and 
partakes  of  the  nature  of  the  other  two.  To  design  branch 
canals  and  distributaries  correctly  it  is  necessary  first  to  con- 
sider what  will  be  the  future  methods  of  water  distribution. 
According  to  the  practice  common  to  almost  all  countries  in 
which  irrigation  is  established,  the  distribution  of  water  is 
effected,  at  any  rate  during  seasons  of  short  supply,  by  some 
system  of  rotation.  Under  such  a  system  water  is  alternately 
supplied  and  withheld  for  certain  fixed  periods,  so  that  each 
distributing  channel  flows  only  for  the  time  required  to  irrigate 
the  crop  depending  on  it,  and  not  during  the  intervals  between 
waterings.  This  method  of  distribution  will  be  fully  described 
in  Chapter  X.,  but  it  is  necessary  to  refer  to  it  here,  as  the 
design  of  the  distributaries  has  to  be  based  on  the  method  to 
be  adopted.  Suppose,  for  instance,  that  the  rotation  pro- 
gramme arranges  that  water  shall  be  supplied  for  seven  days 
and  be  cut  off  for  the  following  seven.  The  discharge,  which 
has  been  calculated  on  the  basis  of  a  continuous  flow,  must, 
under  such  a  supposition,  be  doubled,  as  it  will  have  to  do  the 
same  amount  of  work  in  half-time.  The  distributaries  of  the 
Ganges  Canal  in  India,  as  originally  designed,  did  not  contem- 
plate any  distribution  by  rotation.  Many  of  them  have,  in 
consequence,  been  lately  remodelled  so  as  to  enable  them  to 


MEANS   OF   DISTRIBUTION.  1ST 

run   every   alternate   week    instead   of    continuously   as   they 
formerly  did. 

In  Egypt,  for  summer  irrigation,  the  distributaries  of  each 
separate  system  are  divided  into  three  groups,  to  each  of  which 
water  is  given  in  succession  for  a  third  of  the  whole  period  of 
rotation,  or  interval  between  waterings.  Therefore,  as  the 
irrigation  has  to  be  effected  in  a  third  of  the  time  that  would  be 
taken  by  a  constant  discharge,  the  distributary  must  be  capable 
of  carrying  three  times  the  discharge  calculated  on  the  basis  of 
a  continuous  flow.  It  has  been  shown  in  Chapter  III.  that  12 
cubic  metres  a  day  per  acre  commanded  is  the  continuous 
discharge  required  to  irrigate  the  summer  crops  of  Egypt, 
assuming  a  watering  every  eighteen  days.  This  being  the 
allowance  for  a  continuous  flow,  the  discharge  required  to 
complete  the  irrigation  in  a  third  of  the  time,  or  six  days,  must 
be  calculated  at  the  rate  of  36  cubic  metres  a  day  per  acre 
commanded  below  the  point  that  is  being  considered. 

On  the  Sone  canals  in  India  closures  of  entire  distributaries 
for  half-time  were  provided  for,  and  the  channels  were  designed 
to  carry  twice  the  volume  which  would  have  been  allowed 
with  a  continuous  flow  discharge.  Mr.  Buckley  considers 
this  period  of  closure  excessive,  and  is  of  opinion  that 
five  days'  closure  in  fifteen  is  sufficient.  Agreement  between 
Indian  and  Egyptian  practice  is  not  to  be  expected.  Irrigation 
problems  in  India  are  more  complicated  than  in  Egypt  on 
account  of  the  greater  variety  and  complexity  of  the  condi- 
tions. In  Egypt,  rainfall,  being  a  negligible  factor,  introduces 
no  complications.  The  fact  also  that  practically  all  cultivable 
land  in  Egypt  is  irrigated,  so  that  the  area  commanded  and 
the  total  area  under  cultivation  are  the  same,  simplifies  many 
questions  of  irrigation.  That  is  why  Egypt  furnishes  so  many 
useful  illustrations  of  irrigation  principles,  the  varying  factors 
of  other  countries  being  eliminated. 

The  best  form  of  distributary  channel  is  found  by  Neville's 
rule  in  this  way:  "  Describe  any  circle  on  the  drawing  board; 


1 82  IRRIGATION. 

draw  the  diameter  and  produce  it  on  both  sides ;  draw  a  tan- 
gent to  the  lower  circumference  parallel  to  this  diameter,  and 
then  draw  side  slopes  at  the  given  inclinations,  touching  the 
circumference  on  each  side  and  terminating  in  the  parallel 
lines.  The  trapezoid  thus  formed  will  be  the  best  form  of 
channel,  and  the  width  at  the  surface  will  be  equal  to  the  sum 
of  the  two  side  slopes."  The  usual  value  to  give  to  the  side 
slopes  of  distributaries  is  i  to  i.  An  ideal  section,  including 
the  banks,  is  given  in  Fig.  53 

Distributaries  should  be  so  designed,  as  regards  their  longi- 
tudinal section,  that  the  lands  served  by  them  may  be  readily 
irrigated  free-flowi  This  principle  has  been  opposed  at  different 

CROSS  SECTION   OF   AN 
IDEAL    DISTRIBUTARY 

FIG    53 


times  by  those  who  have  maintained  that  lift  irrigation  is 
the  healthy  system,  and  flush  irrigation  the  reverse.  Water- 
logging of  the  soil  and  salt  efflorescence  have  resulted  from  the 
long-continued  maintenance  of  canal  water  levels  above  country 
surface.  The  remedy  for  these  evil  effects  of  infiltration  was 
held  to  be  a  permanent  lowering  of  the  canal  water  levels,  and 
a  resort  to  lift  irrigation.  But  neither  India  nor  Egypt  has 
accepted  this  view.  The  advantages  of  flow  irrigation  are  as 
obvious  as  the  ill  effects  of  infiltration.  The  system  to  be 
preferred  is  one  that  will  avoid  the  ill  effects  without  losing 
the  advantages.  The  first  condition  for  a  healthy  system  is 
effective  drainage  at  all  times.  When  that  has  been  secured, 
no  harm  will  come  of  high  levels  in  the  canals,  provided  they 
are  produced  for  short  periods  alternating  with  equal  or  longer 
periods  of  low  levels.  With  these  provisoes  an  easy,  cheap,  and 


MEANS   OF   DISTRIBUTION.  I&3 

plentiful  water  supply  is  an  unmixed  blessing  to  agriculture. 
A  liberal  supply  of  water,  combined  with  a  perfect  system  of 
drainage,  will  provide  the  means  for  washing  salt  out  of  the 
soil  that  is  impregnated  with  it,  if  the  water  is  delivered  free- 
flow. It  would  be  useless  to  attempt  such  washings  where 
water  has  to  be  lifted,  as  it  would  not  pay.  To  prevent  any 
harmful  effect  from  infiltration  due  to  high  levels,  the  canals 
should  be  run  at  high  and  low  levels  alternately.  The  system 
of  irrigation  by  rotation  lends  itself  to  this  arrangement.  Such 
an  alternating  or  intermittent  supply  keeps  the  water  in  the 
soil  from  stagnating,  gives  free-flow  during  the  high  level 
period,  and  affords  relief  to  the  drains  during  the  low  periods 
by  reducing  the  excess  resulting  from  wasteful  irrigation.  The 
canals  also  themselves,  when  low,  act  as  drains  to  those  lands 
alongside  them  which  have  imbibed  too  freely  during  the  high 
level  period. 

There  is  another  reason  for  designing  the  distributing  canals 
so  that  they  may  deliver  their  water  free-flow.  During  the 
floods  of  certain  rivers  the  water  carries  along  with  it  rich 
fertilising  matter,  brought  down  from  the  hills  or  catchment 
basins  where  the  rains  which  cause  the  floods  fall.  It  is  most 
desirable  to  secure  on  the  fields  as  much  of  this  silt  as  possible. 
Therefore,  during  flood,  the  canals  should  be  run  with  liberal 
supplies,  and  at  such  levels  that  the  water  can  be  readily  made 
use  of.  But  there  must  be  limits  to  this  liberality,  as,  other- 
wise, either  the  drains  will  have  to  be  made  extravagantly 
large,  or  they  will  be  called  upon  to  do  more  work  than  they 
can  efficiently  perform.  The  alternation  of  weeks  of  high 
level  and  of  reduced  supply — not  necessarily  low  supply — 
seems  to  afford  the  most  convenient  compromise  that  gives 
the  advantage  of  a  sufficiently  liberal  supply  without  the 
detracting  accompaniment  of  bad  drainage. 

The  distributaries,  therefore,  must  be  designed  to  give  free- 
flow irrigation  when  running  full  supply.  Under  the  rotation 
system  they  irrigate  only  when  at  full  supply.  A  suitable  full 


1 84  IRRIGATION. 

supply  level  for  the  water  of  a  distributary  will  then  be  repre- 
sented by  a  line  approximately  parallel  to  the  land  surface  and 
about  a  foot  above  it. 

Those  branch  canals  which  perform  the  duty  of  direct 
irrigation  should  be  designed  as  if  they  were  distributaries; 
while  those  that  act  in  the  same  way  as  main  canals,  that  is, 
merely  as  carriers  of  water  to  the  heads  of  the  distributing 
channels,  should  be  reckoned  main  canals. 

The  application  of  the  foregoing  principles  may  be  illustrated 
by  taking  the  case  of  the  distributing  canals  of  the  delta  of 
Egypt.  During  the  period  of  short  supply  in  summer  a  three- 
section  rotation  is  applied ;  that  is,  each  of  the  three  sections 
into  which  separate  canal  systems  are  divided  has  water  for  a 
third  of  a  rotation  period  (or  interval  between  successive 
waterings),  and  is  without  it  for  two- thirds.  If  the  full  period 
is  fixed  at  eighteen  days,  each  section  gets  water  for  six  days 
and  is  without  it  for  twelve.  As  has  been  already  shown,  the 
distributing  canals  must  carry  during  their  supply  period  a 
discharge  calculated  at  the  rate  of  36  cubic  metres  per  day  per 
acre  commanded.  During  the  flood  season  the  programme  is 
altered.  The  distributing  canals  are  given  full  and  reduced 
supply  in  alternate  weeks.  The  allowance  in  flood  is  at  the 
rate  of  25  cubic  metres  per  day  of  continuous  flow  per  acre 
commanded.*  If  the  flood  rotation  programme  provided  for  the 
whole  volume  being  delivered  in  one  half-period,  and  nothing  in 
the  other  half-period,  the  channels  would  have  to  carry  50  cubic 
metres  per  day  per  acre  for  half-time.  As  this  figure  is  greater 
than  the  summer  discharge  of  36  cubic  metres,  this  larger  flood 
discharge  would  determine  the  dimensions  of  the  canals. 
But  it  has  been  found  undesirable  to  reduce  the  discharge  to 
nothing  in  one  half-period,  and  better  for  the  general  conve- 
nience to  arrange  that  the  discharge  of  the  low  period  may  be 
about  half  the  discharge  of  the  high  period.  Thus  the  high 
period  discharge  would  be  at  the  rate  of  33  cubic  metres,  and 
the  low  period  discharge  at  the  rate  of  17  cubic  metres,  per  day 


MEANS  OF   DISTRIBUTION.  185 

per  acre.  As,  however,  the  summer  programme  requires  that 
the  canals  shall  be  able  to  carry  a  discharge  at  the  rate  of 
36  cubic  metres  per  day  per  acre,  this  figure,  being  the  larger, 
determines  the  dimensions  of  the  canals,  and  represents  full 
supply.  The  distributing  canals  during  the  flood  would  then 
run  full  supply  one  week,  and  at  reduced  supply,  or  at  the  rate 
of  (50  —  36  =)  14  cubic  metres  per  day  per  acre,  the  alternate 
week. 

Summing  up  the  results  obtained  in  the  particular  illustra- 
tion chosen,  the  main  canals  (and  branch  canals  serving  as 
carriers  only)  would  be  designed  to  carry  a  continuous  dis- 
charge calculated  at  the  rate  of  25  cubic  metres  a  day  per  acre 
commanded  ;  the  distributaries  (and  branch  canals  acting  as 
distributing  channels)  would  be  designed  to  carry  a  maximum 
discharge  calculated  at  the  rate  of  36  cubic  metres  a  day  per 
acre  commanded.  The  flow  of  the  latter  in  summer  would  be 
intermittent,  the  water  being  cut  off  for  periods  equal  to  double 
the  duration  of  the  periods  of  supply.  In  the  flood  season  the 
canals  would  flow  alternately  at  full  and  half-supply  for  equal 
periods. 

This  example  is  no  more  than  an  illustration  of  the  appli- 
cation of  principles  to  a  particular  case.  Every  country  will 
have  its  own  peculiar  conditions  which  will  determine  how 
the  principles  of  design  should  be  adapted  to  its  convenience 
and  advantage. 

A  scheme  of  drains  should  form  part  of  the  original  project 
for  the  irrigation  of  any  tract  of  country  that  includes  low- 
lying  lands.  But  it  can  scarcely  be  said  that  this  rule  has  been 
followed  in  the  past  in  those  countries  where  irrigation  has 
been  practised.  The  history  of  irrigation  shows  rather  that 
canals  have  first  been  made  and  used  for  a  long  time  before 
any  attention  has  been  paid  to  drainage.  It  was  assumed  that 
it  could  take  care  of  itself,  and  that  rainfall  and  the  surplus 
water  of  irrigation  would  disappear  somehow  by  evaporation, 


186  IRRIGATION. 

absorption,  or  otherwise.  To  some  extent,  in  high-lying  lands, 
drainage  will  take  care  of  itself  provided  the  natural  drainage 
channels  are  not  interfered  with.  But  in  low-lying  lands  the 
evils  that  result  from  neglect  of  drainage  will  inevitably  call 
attention  to  the  subject.  The  postponement  of  its  considera- 
tion until  after  the  canals  have  been  made  is  now  recognised  as 
wrong  in  principle.  This  does  not  mean  that  a  complete 
system  of  drains  should  be  laid  down  at  the  time  of  the 
carrying  out  of  an  irrigation  project.  But  the  main  drains  and 
branches,  and  all  drains  in  fact  which  it  is  certain  will  be 
necessary,  should  be  included  in  the  scheme.  The  necessity 
for  additional  drains  will  doubtless  arise  as  the  irrigation 
develops,  but  they  can  be  made  when  the  want  of  them  is  felt. 
The  history  of  the  construction  of  the  Ganges  Canal  in  India 
and  its  subsequent  remodelling  to  provide  for  drainage,  which 
had  been  disregarded  in  the  first  instance,  forms  an  instructive 
lesson  for  irrigation  engineers.  In  Egypt  twenty  years  ago 
there  were  no  drains,  and  much  land  had  been  ruined  for  want 
of  them,  and  more  was  in  process  of  being  ruined.  Since  then 
hundreds  of  miles  of  drains  have  been  dug,  and  not  only  is 
the  further  spread  of  the  evil  stopped,  but  the  lands  that  were 
ruined  are  being  reclaimed  to  cultivation.  In  the  west  of  the 
United  States  the  same  mistake  was  made  as  had  been  made 
before  in  Egypt:  natural  drainage  lines  were  converted  into 
irrigation  channels,  with  the  inevitable  result  of  waterlogging 
the  soil  and  rendering  it  uncultivable.  The  San  Joaquin 
valley  in  California  has  suffered  from  this  injurious  practice. 
Most  countries,  in  short,  which  have  occupied  themselves  with 
irrigation,  have  learnt  sooner  or  later  that  drainage  also  must 
receive  its  due  share  of  attention. 

A  drain  to  be  efficient  must  be  designed  with  a  waterway 
of  such  levels  and  dimensions  that  it  will  carry  away  the 
surplus  water  of  the  area  served  by  it,  with  a  water  surface 
always  well  within  soil.  The  water  level  in  the  drain  should, 
if  possible,  be  kept  at  least  2  feet  below  land  surface.  The 


MEANS  OF   DISTRIBUTION.  187 

maximum  discharge  which  should  be  provided  for  will  be  pro- 
portional to  the  area  to  be  drained,  and  will  depend  on  the 
rainfall  as  well  as  on  the  description  of  irrigation  practised. 
Land  under  rice  crops  discharges  at  least  double  the  amount 
that  land  under  ordinary  crops  does.  If  the  rainfall  is  con- 
siderable it  is  probable  that  land  depressions  will  be  well 
marked  and  be  traversed  by  natural  drainage  lines  which  may 
take  the  place  of  the  main  drains  of  an  artificial  system.  But,  if 
that  is  not  the  case,  the  main  drains,  as  well  as  subsidiary 
drains,  must  have  sufficient  discharging  capacity  to  carry  away 
both  rainfall  and  excess  canal  water.  It  is,  of  course,  impossible 
to  lay  down  what  allowance  must  be  made  for  rainfall  when  the 
conditions  are  not  known.  The  amount  of  rainfall,  its  intensity 
for  short  periods,  the  season,  the  soil,  the  configuration  of  the 
ground,  all  affect  the  question,  and  must  be  taken  into  account 
when  the  drainage  scheme  is  being  elaborated. 

Neglecting  the  question  of  rainfall,  it  is  possible  to  state  the 
principles  on  which  the  drains  should  be  designed  to  enable 
them  to  carry  off  the  surplus  water  resulting  from  irrigation. 
A  system  of  drains  is  the  converse  of  the  system  of  canals  with 
which  it  is  associated.  The  main  drain,  which  forms  the  tail 
of  the  drainage  system,  corresponds  with  the  main  canal  that 
forms  the  head  of  the  irrigation  system ;  the  subsidiary  drains 
correspond  to  the  distributing  irrigation  channels.  As  the 
main  canal  carries  water  to  the  channels  which  distribute  it,  so 
the  main  drain  carries  away  the  water  which  the  subsidiary 
drains  collect  and  discharge  into  it.  The  discharge  of  the 
main  drains  will  be  more  or  less  constant  for  prolonged  periods, 
as  the  total  drainage  of  a  large  extent  of  country  is,  on  the 
average,  the  same  throughout  a  season.  In  correspondence 
with  the  irrigation  periods  of  rotation,  the  flow  in  branch  drains 
will  be  intermittent.  Some  will  be  discharging  at  one  time 
and  some  at  another,  so  that  those  that  are  discharging  are 
balanced  by  those  that  have  ceased  to  discharge,  and  the 
aggregate  discharge  of  all  the  collecting  drains  of  a  system 


188  IRRIGATION. 

becomes  a  fairly  constant  quantity.  H~nce  the  dimensions  of 
the  main  drain  should  be  calculated  on  the  basis  of  a  con- 
tinuous flow.  The  question  is,  what  discharge  per  acre  of  land 
served  by  the  drain  must  be  allowed  in  order  to  arrive  at  the 
amount  of  run-off.  The  maximum  discharge  to  be  admitted 
into  the  canal  system  for  the  purpose  of  irrigation  will  have 
been  previously  determined  as  the  basis  on  which  the  canals 
were  designed.  The  maximum  discharge  in  any  drain  should 
naturally  be  something  less  than  the  maximum  admitted  into 
the  canals.  For  a  main  drain,  below  the  inflow  of  the  lowest 
branch  drain,  it  would  probably  be  sufficient  to  provide  for  a 
third  of  the  irrigation  maximum.  This  allowance  would 
contemplate  a  continuous  flow.  But  on  the  branch  drains  the 
discharge  becomes  more  intermittent  and  fitful  the  higher  in  the 
system  the  drain  may  be.  For  this  reason  the  minor  drains  must 
be  allowed  a  comparatively  large  section,  as  they  will  have  to 
carry  off  the  water  as  it  reaches  them,  that  is,  in  half  time  or 
third  time.  In  the  case  of  the  main  drain  a  third  of  the  irriga- 
tion volume  was  assumed  to  run  off,  but  in  the  case  of  the  minor 
branch  drains  at  the  upper  extremity  of  the  drained  area  it  is 
well  to  calculate  that  half  the  maximum  irrigation  allowance 
per  acre,  used  to  determine  the  dimensions  of  the  distribu- 
taries, may  have  to  be  carried  by  the  drain  at  some  time 
or  other.  The  drains  which  are  intermediate  between  the 
uppermost  branches  and  the  main  drain  would  be  given  sections 
capable  of  discharging  volumes  calculated  at  a  rate  per  acre 
which  would  be  less  than  that  used  for  designing  the  minor 
branch  drains  above  them,  but  greater  than  that  provided  for 
by  the  dimensions  of  the  main  drain. 

As  the  delta  of  Egypt  has  furnished  an  illustration  for 
canal  design,  it  will  be  useful  to  complete  the  example  by 
applying  the  foregoing  principles  to  its  drainage  system.  For 
this  purpose  Egypt  is  the  most  favourable  instance  to  select, 
since,  as  has  already  been  stated,  its  rainfall  is  negligible  and  the 
whole  area  commanded  is  irrigated.  The  maximum  discharge 


MEANS   OF   DISTRIBUTION.  189 

admitted  into  the  main  canals  is  at  the  rate  of  25  cubic  metres 
a  day  per  acre  commanded.  Therefore  the  main  drain,  which 
should  carry  about  a  third  as  much,  will  be  designed  to  dis- 
charge at  the  rate  of  8  cubic  metres  a  day  per  acre  served  by  it. 
The  distributing  canals  are  designed  to  carry  a  maximum  of 
36  cubic  metres  a  day  per  acre  commanded.  The  minor  branch 
drains  at  the  upper  end  of  the  drainage  system,  which  should 
carry  half  as  much,  will  be  designed  to  discharge  at  the  rate  of 
18  cubic  metres  a  day  per  acre  served  by  them.  The  inter- 
mediate drains,  according  to  their  position  on  the  drainage 
system  to  which  they  belong,  should  be  made  capable  of 
carrying  15,  12,  and  10  cubic  metres  a  day  per  acre. 

Deep  drains  are  preferable  to  shallow  ones,  as  weeds  grow 
less  readily  in  the  former.  Drain  water,  being  clear,  encourages 
the  growth  of  weeds,  whereby  the  efficiency  of  drains  is  often 
much  diminished.  A  low  rate  of  velocity  is  also  favourable  to 
weed  growth.  It  is  therefore  better  to  give  depth  of  channel 
in  preference  to  width  to  the  extent  that  is  practicable,  and 
also  to  give  a  comparatively  steep  gradient  to  the  drain  so  as 
to  secure  a  high  velocity  of  flow.  This  latter  is  often  impossible, 
especially  in  main  drains  near  their  outfalls  if  the  land  which 
they  drain  is  flat.  Depth  of  channel  must  then  be  relied 
upon  to  discourage  weed  growth.  In  large  systems  the  main- 
tenance of  the  depth  can  only,  as  a  rule,  be  arranged  for  by 
dredging.  To  secure  a  sufficient  depth  and  velocity  of  flow 
fur  the  continuous  discharge  of  the  main  drain,  it  is  necessary 
to  avoid  giving  the  channel  excessive  dimensions.  If  the 
discharging  capacity  of  the  drain  is  just  sufficient,  but  no 
more  than  sufficient,  so  that  it  will  carry  away  the  drainage 
water  with  a  depth  that  will  prevent  weed  growth,  the 
drain  will  maintain  its  efficiency  for  a  longer  period  than 
it  would  do  if  it  were  of  larger  section  and  flowed  with 
less  depth. 


CHAPTER  IX. 

MASONRY    WORKS   ON    IRRIGATION    CANALS. 

MASONRY  works  are  required  on  the  distributing  channels  of 
an  irrigation  system  to  give  effective  control  over  the  supply 
and  its  distribution.  They  may  be  classified  as  follows : — 

(1)  Regulating  works  to  distribute  the  water  and  control  its 
levels,  such  as  head  sluices,  regulators,  escapes,  and  culverts  ; 

(2)  Works   to    overcome    an    abrupt   and   decided   change 
of  level  in   the   canal    system,    such    as   falls   and   rapids  or 
cascades ; 

(3)  Works  to  provide  for  crossing   drainage  lines,  such  as 
aqueducts  and  syphons; 

(4)  Road  bridges  at  traffic  crossings. 

The  head  sluice  of  a  canal  controls  its  supply.  In  the 
preceding  chapter  it  was  pointed  out  that,  to  meet  the  silt  diffi- 
culty, the  head  sluice  of  a  main  canal  fed  from  a  muddy  river 
should  be  given  a  considerable  length  and  a  raised  sill,  and  that 
the  shutters  should  be  worked  in  such  a  way  as  to  admit  only 
the  upper  water.  Mr.  Buckley,  who  was  an  advocate  of  these 
principles  and,  as  chief  engineer  of  Bengal,  a  practical  demon- 
strator of  their  soundness,  gives  the  following  description  of  the 
Trebeni  Canal  head  sluice  (Fig.  54) : — 

"  The  Trebeni  Canal  head  sluice,  which  is  now"  (1905)  "under 
construction  in  Bengal,  stands  on  the  bank  of  the  Gunduk  river, 
at  a  point  where  the  flood  rises  over  20  feet.  The  sluice  is 
designed  to  give  the  required  discharge  with  a  depth  of  2  feet 
of  water  flowing  over  the  tops  of  hurries  or  horizontal  baulks. 
The  vents  A  A  have  draw-gates,  worked  by  a  screw  and  capstan 
on  the  parapet.  These  vents  will  be  used  to  some  extent  for 


MASONRY  WORKS  ON    IRRIGATION    CANALS. 


regulation,  and  will  be  closed  entirely  if  the  high  floods  carry 
down  heavy  silt,  which  would  be  likely  to  choke  the  canal. 
When  the  flood  level  is  more  than  2  feet  above  969-50  the 
supply  will  be  drawn  in  over  the  top  of  the  arch  platform  which 
lies  at  that  level.  At  that  time  the  vents  B  B  and  C  C  will  be 
entirely  closed.  As  the  flood  falls  below  the  platform  the 
hurries  in  the  vents  B  B  will  be  removed,  as  required,  and 
the  water  will  be  drawn  in  over  the  top  of  them  into  the  canal. 
When  the  water  level  in  the  river  falls  to  less  than  2  feet  above 
the  top  of  the  platform  at  961*00  the  kurries  in  the  vents  C  C 


TREBENI  CANAL  HEAD  SLUICE 

Scale 

.060       10 20 30 *0 


Feet 


FJ.Q    54 


Hill  be  lemoved,  as  required,  and  the  discharge  will  be  regulated 
over  the  tops  of  the  kurries  in  those  vents." 

This  is  an  excellent  example  of  the  application  of  the  prin- 
ciples on  which  a  head  sluice  should  be  designed  with  the 
object  of  excluding  heavy  silt  from  a  canal."  In  this  case  there 
is  no  raised  sill,  but  the  whole  floor  is  3  feet  above  the  canal 
bed  level.  There  are  twenty-two  vents  in  this  sluice,  each 
6  feet  wide  at  A,  7  feet  at  B,  and  7  feet  6  inches  at  C. 

Vents  of  head  sluices  vary  in  width  from  3  feet  to  16  feet, 
In  Egypt  the  head  sluices  of  the  largest  canals  have  vents  of 
5  metres  (16  feet  5  inches)  width.  The  waterway  allowed  is 
determined  by  the  discharge  required  and  the  available  head  at 


192  IRRIGATION. 

different  seasons,  it  is  a  good  rule  to  allow  a  liberal  waterway 
with  a  margin  for  meeting  the  demand  for  an  increased  dis- 
charge which  future  developments  may  create.  The  extra 
allowance,  beyond  the  area  calculated  to  be  necessary, 
might  conveniently  amount  to  10  per  cent,  in  large  works  and 
25  to  30  per  cent,  in  smaller  works.  The  floor  of  a  head  sluice 
and  its  up-stream  and  down-stream  aprons  will  have  to  resist  the 
same  forces  and  be  subjected  to  the  same  action  as  a  river 
barrage,  described  in  Chapter  VI.,  and  therefore  should  be 
similar  in  design.  Two  large  head  sluices,  lately  built  at 
Assiout  and  Zifta,  in  Egypt,  have  been  given  practically  the 
same  cross-section  as  the  river  barrages  with  which  they  are 
associated.  Head  sluices,  however,  with  narrower  vents,  and 
at  the  head  of  branch  canals,  can  be  built  of  lighter  construc- 
tion than  head  sluices  on  a  river,  as  the  up-stream  water  level  is 
not  subject  to  such  great  variation  in  a  feeder  canal  as  it  is  in 
a  river.  The  design  of  the  superstructure  depends  to  a  great 
extent  on  the  description  of  regulating  apparatus  adopted,  and 
sometimes  on  the  necessities  of  the  traffic  that  will  pass  over 
the  sluice.  The  different  forms  of  regulating  apparatus  will  be 
referred  to  later  in  this  chapter. 

In  a  general  way  the  principles  of  design  are  the  same  for 
all  canal  works  of  regulation  which  are  subjected  to  a  head  of 
water  up  stream  and  to  scouring  action  down  stream.  The  head 
or  the  scour  may  be  greater  or  less,  necessitating  a  modifica- 
tion of  the  design  in  those  dimensions  which  are  affected  by  the 
one  or  the  other.  An  escape  or  fall,  as  a  rule,  requires  ample 
protection  down  stream  in  the  form  of  an  extension  of  the  floor, 
well-revetted  slopes,  and  a  talus  of  heavy  pitching,  inasmuch 
as  a  heavy  discharge  through  it  may  continue  to  work  under 
an  undiminished  head  for  some  time ;  whereas  in  the  case  of 
a  simple  regulator,  the  canal  below  quickly  fills  up,  and  the 
head  is  reduced.  A  basin  regulator  in  a  cross  embankment 
works  under  the  conditions  of  an  escape  or  fall,  as  it  discharges 
into  an  open  basin  requiring  an  enormous  volume  of  water  to 


MASONRY  WORKS  ON    IRRIGATION   CANALS.  193 

affect  its  surface  level.  It  is  therefore  necessary  to  give  the 
same  attention  to  the  down-stream  protection  of  basin  regulators 
as  is  required  in  the  case  of  escapes. 

Regulators  are  generally  placed  where  a  canal  bifurcates,  and 
below  the  point  where  a  branch  canal  takes  off.  They  may 
also  be  required  across  a  canal  immediately  below  an  escape  or 
level  crossing.  They  are,  in  fact,  necessary  or  desirable  wherever 
a  division  of  the  water  supply  has  to  be  made. 

Escapes  are  the  safety  valves  of  a  canal  system.  They 
supply  the  means  of  disposing  of  any  surplus  discharge  that  has 
to  be  got  rid  of,  when,  for  instance,  in  consequence  of  a 
slackening  of  the  demand  for  water,  the  irrigating  sluices  are 
suddenly  shut  down.  This  often  occurs  after  a  heavy  fall  of 
rain  without  sufficient  warning  for  the  situation  to  be  met  by 
decreasing  the  discharge  entering  the  canal  at  its  head.  Escapes 
are  also  useful  in  case  of  an  accident  to  any  of  the  canal  works 
requiring  an  immediate  reduction  of  the  discharge.  They  also 
assist  in  producing  a  high  enough  velocity  in  the  canal,  when 
it  is  carrying  muddy  flood  water,  to  lessen  silt  deposit,  and, 
later  on,  when  the  water  is  clear  and  a  surplus  available,  they 
make  it  possible  to  maintain  a  high  current  in  the  canal  whereby 
silt  deposits  that  have  formed  during  flood  are  diminished  by 
scour.  For  these  purposes  escapes  are  most  desirable  on  main 
canals  and  long  distributaries,  not  only  at  the  tails,  but.  at 
intervals  along  their  courses. 

If  possible,  an  escape  should  discharge  into  a  river  or  well- 
defined  waterway,  and  not  into  a  drainage  line.  This  principle, 
however,  cannot  always  be  carried  out,  and  something  short  of 
the  ideal  has  to  be  accepted :  a  river  may  not  be  within  reach, 
and  no  well-defined  waterways,  other  than  drainage  lines,  may 
offer  themselves. 

The  design  of  an  escape  may  be  similar  to  that  of  a  head 
sluice,  a  regulator,  or  a  fall,  or  a  combination  of  them.  But, 
as  already  stated,  the  down-stream  protection  must  be  adequate. 
An  escape  may  take  the  form  of  a  waste  weir  with  a  drop,  and 

I.  o 


194 


IRRIGATION. 


be  protected  down  stream  by  a  "  rapid  "  or  "  cascade,"  the  fall 
of  the  water  being  divided  between  the  drop  of  the  weir  and  the 
rapid  forming  its  apron.  On  the  crest  of  the  drop-wall,  shutters 
or  baulks  or  other  regulating  devices  would,  if  necessary,  control 
the  volume  escaped. 

Basin  escapes  which  have  to  pass  large  quantities  of  water 
are  sometimes  formidable  works.  There  is  a  fine  work  in 
Egypt,  of  modern  construction,  known  as  the  Kosheshah  escape. 
It  was  designed  to  discharge  back  into  the  Nile  the  contents  of 
a  chain  of  inundation  basins  of  an  aggregate  area  of  555,000 


KOSHESHAH     ESCAPE 


Scale 

10       20 


Feet 


FIG       55 


acres.  It  is  capable  of  discharging  80,000  cubic  feet  a  second 
under  a  maximum  head  of  nearly  15  feet.  It  has  sixty  uppei 
vents  and  sixty  lower  ones  of  the  dimensions  shown  in  Fig.  55. 
The  lower  vents  are  regulated  by  iron  sluice-gates  moved  in 
vertical  grooves  by  an  overhead  winch.  They  are  used  to 
admit  water  into  the  basins  during  the  rise  of  the  flood  and 
afterwards  to  assist  in  emptying  them.  The  upper  vents  are 
used  only  for  the  emptying.  The  latter  are  fitted  with  falling 
gates  hinged  at  their  lower  edges.  A  water  cushion  is  provided 
for  the  gates  to  fall  upon  by  giving  the  upper  floor  a  raised  sill 
of  ashlar  along  its  down-stream  margin.  The  upper  falling 
gates  can  all  be  let  go  within  a  quarter  of  an  hour  if  desired. 


KOSHESHAH    ESCAPE. 


MASONRY  WORKS  ON   IRRIGATION   CANALS.  IQ5 

The  object  of  providing  for  quick  opening  is  to  produce  a  wave 
in  the  river  after  a  poor  flood  so  as  to  submerge  certain  high 
islands  and  river-side  lands  which  depend  on  the  flood  rise  for 
their  irrigation  but  are  of  too  high  a  level  to  be  reached  by 
poor  floods.  The  artificial  wave  created  by  the  sudden  empty- 
ing of  the  basin  contents  back  into  the  Nile  has  often  succeeded 
in  effecting  the  irrigation  which  the  natural  flood  had  failed  to 
complete.  Plate  VIII.  gives  a  view  of  part  of  the  Kosheshah 
escape  taken  during  construction  but  after  the  masonry  had  been 
completed.  The  bottom  gates  were  already  in  their  grooves, 
closing  the  lower  vents,  and  an  upper  gate  was  being  put  in 
place  when  the  photograph  was  taken.  In  the  bay  to  the  left 
of  the  one  where  the  gate  is  being  hung  both  the  upper  and 
lower  gates  are  in  position,  closing  the  vents  ;  in  the  bay  to  the 
right  the  upper  gate  is  wanting. 

Canal  falls  or  weirs  are  required  at  intervals  along  a  canal 
which  has  a  gradient  that  is  less  than  the  slope  of  the  country 
through  which  it  runs.  If  the  canal  is  navigable,  wherever 
such  falls  are  necessary  a  lock  has  to  be  provided  for  passing 
boats  between  the  upper  and  lower  reaches. 

The  once  favoured  form  of  "  ogee  "  fa1!  has  been  generally 
condemned,  as  falls  of  this  description  have  given  endless 
trouble,  the  principle  of  design  being  a  mistaken  one.  "Falls" 
are  now  usually  given  a  vertical  drop  wall  with  a  steep  face 
batter.  There  are  various  ways  of  providing  resistance  to  the 
shock  of  the  falling  water.  The  simplest  way,  and  sometimes 
the  most  economical,  is  to  protect  the  weir  floor,  where  the  water 
falls,  with  a  layer  of  hard  ashlar  sufficiently  strong  to  bear  the 
shock,  the  floor  surface  being  at  the  canal  bed  level  of  the  lower 
reach.  Sometimes  a  cushion  of  water  is  formed  by  building  a 
raised  sill  along  the  down-stream  edge  of  the  floor.  When  this 
arrangement  is  adopted,  the  general  floor  surface  may  be  at 
canal  bed  level  and  the  sill  be  above  it.  But  it  is  more  usual 
to  sink  the  floor  and  to  make  the  crest  of  the  sill  coincide  with 
the  canal  bed,  as  in  Fig.  56.  Sometimes  the  cushion  of  water 

O   2 


196 


IRRIGATION. 


is  formed  by  sinking  the  floor  immediately  below  the  fall  and 
sloping  it  up  to  the  level  of  the  canal  bed  at  the  down-stream 
edge  of  the  floor,  as  in  Fig.  57.  In  the  case  of  weirs  on  navi- 
gable canals  the  crest  of  the  drop  wall  is  often  raised  above  the 
canal  bed  level  of  the  upper  reach,  and  the  water  level  is  some- 
times also  regulated  by  planks  sliding  in  iron  or  masonry 
grooves  above  the  weir  crest,  as  in  Fig.  56. 

On  the  Bari  Doab  Canal  in  India  many  of  the  drops  of  the 

CANAL    FALL 

CUSHION 


WITH    WATER 

Scale 

tO    5      0  10  20 


feet 


W.I 


NOTCH    FALL 

ON    A    CANAL    IN    INDIA 
FIQ     57 


canal  bed  are   effected  by  rapids.     They  are  constructed  of 
boulder  pitching  confined  in  rectangular  spaces  by  longitudinal 
and  cross  walls  of  masonry.     The  surface  boulders  are  bedded 
in  hydraulic  mortar  up  to  their  shoulders  and  are  seated  on  a 
foundation  of  boulders  in  mortar.     The  change  of  bed  level  is 
effected  by  a  rapid  with  a  continuous  flat  surface  slope  of  i  in  15. 
Below  all  falls  there  is  always  the  effect  of  eddies  and  high 
velocity  currents  to  be  overcome.      Various  forms  of  down- 
stream wings,  of  pitched  apron,  and  of  revetted  side  slopes  are 


MASONRY  WORKS  ON   IRRIGATION   CANALS.  197 

adopted  by  different  designers.  There  are  convex  and  concave 
wings,  wings  splayed  at  all  angles,  and  wings  parallel  to  the  direc- 
tion of  flow.  For  the  pitched  length  beyond  the  masonry  work 
there  was,  not  long  ago,  considered  to  be  virtue  in  the  soda- 
water  bottle  form  of  a  more  or  less  pronounced  curvature.  In 
Egypt  there  are  a  great  many  escapes  and  regulators  working 
under  considerable  heads,  which,  having  been  allowed  their 
own  way,  have  scoured  out  deep  and  wide  pools  down  stream 
of  the  floor,  to  the  danger  of  the  whole  work.  The  best  remedy 
for  this  has  been  found  to  be  to  make  dry  rubble  spurs  parallel 
to  the  direction  of  flow,  taking  off  from  the  wings.  The  crest 
of  the  spur  is  usually  at  or  near  high  water  level  at  its  meeting 
with  the  wing,  whence  it  slopes  gently  downwards.  Its  length 
depends  upon  circumstances.  The  result  of  making  these  spurs 
in  many  cases  has  been,  not  only  to  stop  erosion  on  the  flanks, 
but  to  cause  the  deep  pool  to  silt  up  to  some  extent.  The 
principle  of  these  guiding  spurs  has  been  consequently  adopted 
in  the  design  of  new  escapes.  The  masonry  apron  and  pitch- 
ing, instead  of  being  horizontal  in  its  longitudinal  section,  is 
often  given  a  slope  downwards  from  the  pier  ends  of  about 
i  in  10,  and  the  pitched  talus  is  continued  at  the  same  slope. 
On  the  apron  in  front  of  either  wing  a  masonry  footing  is  built 
to  prevent  the  stone  spur  from  sliding  on  the  floor,  and  the  dry 
rubble  spurs  are  constructed  as  above  described.  In  India  the 
place  of  the  dry  rubble  spurs  is  taken  by  dwarf  walls  of 
masonry.  Straight  wings  with  rounded  angles  at  the  return 
walls,  or  wings  with  a  slight  splay  of,  say,  30  degrees  inclina- 
tion to  the  direction  of  flow,  are  preferred  by  some  to  other 
forms. 

A  distinction  must  be  made  between  escapes  which  discharge 
into  open  basins,  or  wide  spaces,  and  ''falls"  in  canals  of  a 
regular  section.  In  the  latter  case,  as  prevention  is  better 
than  cure,  the  works  should  be  designed  to  prevent  pooling. 
It  is  best  to  hold  the  water  in  check  and  to  forcibly  keep  it  to 
its  ordained  channel  until  it  ceases  to  be  turbulent.  To  allow 


IRRIGATION. 


it  to  spread  horizontally  encourages  the  formation  of  eddies. 
Whether  there  is  anything  gained,  beyond  a  water  cushion  to 
break  the  falling  water,  by  sloping  the  floor  and  talus  down- 
wards is  doubtful,  as  vertical  eddies  are  no  more  to  be  desired 
than  horizontal  ones. 

However,  the  form  of  floor  shown  in  Fig.  57  is  stated  by 
Mr.  Buckley  to  be  peculiarly  suitable  for  checking  the  ebulli- 
tions of  the  water  and  reducing  it  to  steady  forward  velocity. 
But  this  form  of  floor  is  used  in  conjunction  with  a  "  notch  * 

FORM    OF     NOTCH 
FOR    CANAL    FALLS 

ELEVATION  SECTION 


FIG    58 


LIP, 


PLAN 


Diamf  b  « 
4  tima    diam- 


fall,  which  works  so  smoothly  that  there  are  no  ebullitions  to 
be  checked.  With  this  description  of  fall  the  difficulties  of 
excessive  velocity  and  great  action  down  stream  have  been 
overcome.  A  sketch  of  one  of  these  notches  is  given  in  Fig.  58 
(from  Buckley).  On  the  Chenab  Canal,  in  India,  falls  have 
been  constructed  of  a  row  of  these  notches  cut  in  a  breast  wall. 
The  principle  of  the  design  is  that  the  notches  discharge  at  any 
given  level  the  same  amount  of  water  approximately  as  the 
canal  above  carries  at  that  level,  so  that  there  is  no  increase  in 
velocity  in  the  canal  as  the  water  approaches  the  fall  (except 


MASONRY  WORKS  ON  IRRIGATION  CANALS. 

for  a  few  feet  close  to  the  notch),  but  a  uniform  flow  and  a 
uniform  depth  is  maintained.  No  heading  up  by  planks  at 
these  falls  is  either  arranged  for  in  the  design  or  permitted. 
They  are,  in  fact,  not  suitable  for  situations  where  heading  up 
is  necessary,  either  for  the  sake  of  navigation  or  for  any  other 
purpose.  The  bases  of  the  notches  of  the  Chenab  Canal 
falls  are  at  the  canal  bed  level  of  the  upper  reach,  and 
the  crest  of  the  breast  wall  is  above  full  supply  level.  At 
the  foot  of  each  notch  there  is  a  lip  projecting  beyond  the 
lower  surface  of  the  breast  wall,  which  has  a  great  influence 
in  spreading  the  stream  and  determining  the  form  of  the 
falling  water. 

In  the  Fayum  Province,  in  Egypt,  the  distribution  of  the 
canal  water  is  to  a  great  extent  effected  by  a  description  of 
weir,  or  rather  collection  of  weirs,  known  as  a  nasbah,  an 
Arabic  word  signifying  "  proportion."  It  is  an  automatic 
distributor  of  the  discharge  of  a  canal  among  its  branches.  It 
is  placed  where  a  channel  divides  up  into  two  or  more  branches, 
and  is  made  up  of  weirs  across  the  heads  of  the  branches  united 
into  one  combined  work.  The  level  of  the  weir  sills  is  the  same 
throughout,  but  the  width  of  the  waterway,  or  length  of  weir 
crest,  in  each  case  is  made  proportional  to  the  area  of  land 
served  by  the  branch.  Provided  that  the  weirs  have  all  a  free  fall 
— that  is,  that  the  level  of  water  in  the  reach  below  the  weir  is 
lower  than  the  sill  of  the  drop  wall — the  distribution  of  water  is 
practically  fair.  The  longer  weirs  pass  rather  more  than  their 
theoretically  correct  discharge ;  but,  as  a  rule,  the  water  pass- 
ing them  has  farther  to  go  to  reach  its  destination  than  that 
which  passes  over  the  shorter  weirs,  and  will  suffer  some  loss 
from  evaporation  and  absorption  on  the  way.  The  arrange- 
ment works  well  and  gives  satisfaction  to  the  cultivators, 
who  are  the  most  interested  in  the  just  distribution  of  the 
water.  The  system  can  only  be  employed  where  the  land 
surface  has  a  slope  sufficient  to  admit  of  the  introduction  of 
free  fall  weirs  at  the  points  of  distribution  in  a  canal.  The 


JOO  IRRIGATION. 

Fayum  is  the  only  province  in  Egypt  where  such  a  system 
is  possible. 

A  most  important  part  of  all  regulating  works  is  the 
apparatus  that  controls  the  levels  and  discharges  of  the 
canals.  In  out-of-the-way  situations,  where  skilled  labour  and 
mechanical  appliances  are  scarce,  simplicity  of  design  is  a 
great  desideratum.  The  earliest  form  of  regulating  apparatus 
was  probably  the  needle  or  vertical  closure,  prevalent  through- 
out Egypt  some  twenty  years  ago,  and  still  common  on  the 
Sind  inundation  canals  in  India.  In  this  system  horizontal 
wooden  baulks  or  rolled  iron  joists,  fixed  in  the  masonry  faces 
of  the  vents,  bear  the  pressure  of  the  vertical  needles.  The 
needles  are  simply  baulks  of  timber  placed  vertically  side  by 
side  across  the  regulator  vents  to  effect  a  total  or  partial 
closure  as  may  be  desired.  They  are  put  in  place  or  removed 
by  some  mechanical  contrivance  overhead.  In  Egypt,  a  few 
years  ago,  this  generally  took  the  form  of  a  lever  of  primitive 
construction,  any  loose  timber  that  was  handy  being  employed  ; 
the  parapet  wall  of  the  regulator  was  made  to  serve  as  the 
fulcrum.  The  needles  were  clumsy,  difficult  to  handle,  and 
unsuitable  where  tight  closures  were  required.  The  system  was 
from  time  to  time  improved  upon  in  its  details.  A  movable  frame 
was  devised  to  carry  the  horizontals  so  that  they  could  be  put 
in  place  when  required.  The  needles  also  were  made  lighter, 
and  were  constructed  with  V-shaped  edges,  like  sheet  planking. 
But,  in  spite  of  these  and  other  improvements,  the  system  of 
closure  by  vertical  needles  has  died  out  in  Egypt,  and  has 
been  replaced  by  the  system  of  closure  by  horizontal  baulks  or 
planks  working  in  vertical  grooves.  The  horizontals  are  easy 
to  handle,  require  few  men  to  work  them,  and  give  a  tight 
closure.  The  pattern  of  plank  which  is  now  generally  used  is 
that  shown  in  Fig.  59.  A  groove  of  8  to  10  inches  depth 
is  required  with  this  description  of  plank  to  give  a  sufficient 
bearing  on  the  full-section  length  between  the  end  hooks, 


MASONRY   WORKS   ON   IRRIGATION    CANALS. 


201 


The  planks  are  raised  by  iron  rods  provided  with  eyes  at  their 
lower  ends  for  engaging  the  hooks.  The  hooks  lie  within  the 
grooves,  so  that  the  rods,  as  they  are  passed  down,  are  sheltered 
from  the  current  flowing  over  the  planks,  and  it  is  therefore  an 
easy  matter  to  feel  for  and  find  the  hook.  The  greatest 
objection  to  the  system  of  horizontals  is  the  difficulty  of 
getting  the  planks  down  in  deep  water  against  a  head.  The 
method  usually  employed  is  to  drop  planks  into  the  grooves 
till  the  top  one  is  above  water,  and  then  to  jump  them  down 
with  an  iron  "  monkey."  The  grooves  in  which  the  planks  work 
are  either  cut  in  ashlar  stone  or  are  of  cast  iron.  It  is  not 

HORIZONTAL    PLANK 

USED   FOR  CLOSURE    IN   EGYPT 


FIG    59 


SPAN>f 


usual  to  employ  this  system  of  horizontal  sleepers,  or  planks, 
for  spans  exceeding  10  feet. 

For  larger  spans  wrought  iron  gates  are  substituted  for  the 
wooden  planks.  But  the  system  is  only  a  modification  of  the 
system  of  closure  by  horizontal  wooden  baulks.  The  gates  slide 
in  cast  iron  grooves  in  the  same  way  as  the  horizontal  planks, 
and  are  raised  and  lowered  by  means  of  travelling  winches 
overhead.  A  suitable  height  for  a  gate  is  8  to  10  feet.  So 
that,  where  the  height  of  closure  is  14  to  20  feet,  a  pair  of 
gates  in  each  opening,  working  in  double  grooves,  is  provided. 
There  are  instances  of  regulators  with  three  gates  and  triple 
grooves  in  each  vent.  Gates  of  this  description  are  provided 
with  rollers  whose  axles  are  fixed  to  the  gates ;  otherwise  the 
weight  of  the  gates  would  not  be  able  to  overcome  the  friction 
when  it  was  desired  to  lower  them  against  a  head.  When  the 


202  IRRIGATION. 

gate  reaches  its  lowest  point  it  ceases  to  bear  on  the  wheels, 
and  slides  on  to  an  inclined  plane  in  the  groove,  so  that  a  tight 
closure  is  secured. 

For  spans  over  18  feet  "  Stoney's "  shutters,  which  are 
counterbalanced  and  move  on  roller  beds,  are  much  in  favour. 
But  their  province  is  rather  rivers  than  canals,  as  canal  regu- 
lators rarely  reach  the  dimensions  of  works  for  which  Stoney's 
gates  are  best  adapted. 

For  the  smaller  canal  regulators,  with  sluice  openings  of 
2  to  6  feet  width,  a  gate  of  wood  or  iron  controls  the  dis- 
charge. Screw  gearing,  with  a  capstan  in  some  form  above, 
is  ordinarily  used  for  lifting  and  lowering  these  gates.  Some- 
times two,  and  even  three,  shutters  in  one  vent  are  operated 
in  the  same  way  by  screw  and  capstan,  the  shutters  sliding 
in  double  or  triple  grooves,  as  in  the  case  of  gates  worked  by 
overhead  winches. 

On  the  Idaho  Canal,  in  the  United  States,  the  Camere 
curtain  of  the  Seine  weirs  is  used  for  regulating  sluices.  It 
is  fitted  to  the  head  of  the  Idaho  Mining  Company's  canal, 
which  has  eight  openings,  8  feet  wide  by  19  feet  high.  The 
roller  curtains,  which  close  the  openings,  are  made  of  steel 
plates  and  angle  iron  to  a  height  of  10  feet  from  the  floor, 
and  of  pine  slats,  6  inches  wide,  above  that  height.  The 
bottom  of  the  curtain  is  fastened  to  a  cast  iron  roller,  on 
which  it  is  wound  up  by  means  of  a  chain  worked  by  an  over- 
head winch.  This  form  of  closure  is  suitable  for  a  sluice  with 
high  vents  where  it  is  desirable  to  keep  the  superstructure  low, 
and  space  for  housing  gates  above  water  level  cannot  be 
conveniently  provided, 

In  the  preceding  chapter,  when  considering  the  alignment 
of  canals,  it  was  laid  down  as  a  general  rule  that  canals  should 
be  so  aligned  as  to  avoid  crossing  natural  drainage  lines  as  much 
as  possible.  But  it  is  not  always  possible  to  avoid  doing  so, 
especially  along  the  first  section  of  tne  canal,  which  lies  between 


MASONRY  WORKS  ON   IRRIGATION  CANALS.  2O3 

the  source  of  supply  and  the  point  where  irrigation  begins. 
It  is  therefore  necessary  to  provide  for  the  passage  or  disposal 
of  the  discharge  of  drainage  lines  or  natural  watercourses 
encountered  by  the  canal.  In  some  cases  their  waters  can 
be  diverted  into  new  courses  and  a  crossing  be  avoided.  But 
when  this  is  not  the  most  advantageous  method,  one  of  the 
following  arrangements  must  be  adopted. 

Local  drainage  of  limited  areas  may  be  discharged  through 
inlets  into  the  canal  if  the  volume  of  water  to  be  got  rid  of  is 
quite  small.  Such  works  are  always  of  little  importance,  as 
it  is  not  permissible  to  deal  with  large  volumes  of  water  in 
this  way. 

Where  the  quantity  of  drainage  water  to  be  dealt  with  is  large, 
it  must  be  provided  with  some  means  of  passing  the  canal  and 
of  flowing  forward  in  its  natural  channel  beyond  the  point  of 
crossing.  A  drainage  line  in  this  connection  signifies  any 
natural  watercourse,  such  as  a  river,  torrent,  or  stream,  which 
carries  the  rainfall  that  drains  off  its  catchment.  There  are 
three  ways  of  arranging  for  the  crossing :  the  drainage  dis- 
charge may  either  pass  into  the  canal  and  out  again  on  the 
opposite  side  by  a  level  crossing  ;  or  it  may  pass  over  the  canal 
by  what  is  called  in  India  a  superpassage ;  or  it  may  pass 
under  an  aqueduct  carrying  the  canal.  The  respective  levels  of 
canal  and  drainage  may  be  such  that  either  of  the  two  latter 
arrangements  may  take  the  form  of  a  syphon,  and  the  terms 
"  superpassage  "  and  "  aqueduct  "  would  no  longer  be  applicable. 
A  superpassage  is  an  aqueduct,  but  irrigation  terminology  in 
India  distinguishes  between  an  aqueduct  that  carries  a  canal 
over  a  drainage  line  and  one  that  carries  drainage  water  over 
a  canal,  the  latter  being  technically  called  a  superpassage. 
The  choice  between  the  different  descriptions  of  work  for  any 
particular  crossing  depends  chiefly  on  the  relative  levels  of  the 
canal  and  the  drainage  channel  and  on  the  respective  cost.  If 
the  canal  is  navigable,  it  must,  of  course,  be  uppermost.  If 
levels  alone  decide  the  matter,  it  would  be  natural  to  adopt  a 


204 


IRRIGATION. 


level  crossing  when  canal  and  drainage  channel  are  at  nearly 
the  same  level,  an  aqueduct  when  the  canal  is  higher  than  the 
drainage,  and  a  superpassage  when  it  is  lower.  If  a  level 
crossing  is  for  any  reason  inconvenient,  the  drainage  can  be 
passed  in  syphon  under  the  canal,  which  is  generally  a  prefer- 
able arrangement  to  passing  the  canal  under  the  drainage, 
but  not  always  so.  There  are  some  situations  in  which 
sudden  floods  may  bring  down  detritus  from  the  hills  of  the 
catchment  and  carry  it  into  the  syphon,  thereby  blocking  the 
waterway.  The  result  may  be  the  destruction  of  the  syphon 
and  the  breaching  of  the  canal.  Under  such  conditions  it 
would  seem  to  be  the  safer  arrangement  to  pass  the  drainage 
in  the  open  channel  above  and  the  canal  in  syphon  below ;  but 
torrents  which  carry  detritus  along  in  any  quantity  will  give 
trouble  in  either  case. 

The  'most  magnificent  specimens  of  aqueducts  at  drainage 
crossings  are  to  be  found  in  India.  The  Solani  and  Nadrai 
aqueducts  are  the  largest  in  the  world.  Mr.  Buckley  gives  the 
following  figures,  which  will  convey  some  idea  of  the  dimensions 
of  these  two  splendid  works  : — 


Solani  Aqueduct. 

Nadrai  Aqueduct. 

River  waterway         ,        .        . 

13,000  square  feet 

.     21,600  square  feet. 

Canal  waterway        * 

i,  600          „ 

.     1,040            „ 

Canal  discharge 

6,780  cusecs 

.     4,100  cusecs. 

Arches  and  spans     .     :r  ';'.       « 

15  of  50  feet    ',v 

15  of  60  feet. 

Width  between  faces 

195  feet    .    ,    .»?.", 

.     148-7  feet. 

Length      ..... 

1,170  feet.        . 

.     1,310  feet. 

Depth  of  foundation  below  river 

bed         

19  feet 

52  feet. 

Total  height      . 

56  feet      . 

.     88  feet. 

Cost           ..... 

32,87,000  rupees 

44,57.000  rupees 

(£219,000). 

(£297,000). 

Time  taken  in  building     . 

7  years     . 

.     4  years. 

The  existing  Nadrai  aqueduct  replaces  its  predecessor,  of 
insufficient  waterway,  which  was  wrecked  by  an  abnormal 
flood.  A  cross-section  and  part  longitudinal  section  of  the 
new  work  is  given  in  Fig.  60.  It  was  originally  intended  to 


MASONRY   WORKS  ON   IRRIGATION   CANALS. 


205 


add  a  sunken  floor  10  feet  below  the  river  bed,  but  during 
construction  it  was  decided  to  omit  this,  except  in  the  two  end 
spans,  as  the  clay  substratum  found  below  the  sand  was  con- 
sidered to  have  sufficient  resistance  to  scour  without  masonry 
protection.  A  protective  floor  is,  however,  often  added  in 
works  of  this  description.  The  Nadrai  aqueduct  will  serve  as 
an  illustration  of  this  type  of  work,  whether  aqueduct  or  super- 
passage.  The  maximum  drainage  discharge  in  the  upper 

NADRAI    AQUEDUCT 

OVER    THE     KALI     NADI 


F  ,  Q      60 


Mote.  Arching     m 

not    shown 


channel  of  a  superpassage  is,  however,  generally  larger  than 
that  of  the  canal  below,  requiring  a  modification  in  the  design 
as  regards  the  relative  dimensions  of  the  upper  and  lower 
waterways.  The  discharge  which  passes  over  the  Budki 
superpassage  in  India  reaches  the  high  figure  of  34,000  cubic 
feet  a  second.  In  the  design  and  construction  of  such  works 
particular  attention  must  be  paid  to  the  wing  walls  and  to  the 
bond  between  the  earthwork  of  the  upper  channel  and  the 
masonry  duct.  The  wing  walls  should  be  given  ample  length, 
and  all  possible  precautions  should  be  taken  to  prevent  any 
creep  of  water  along  their  faces  from  the  upper  to  the  lower 


2O6  IRRIGATION. 

channel,  as  any  such  defect  would  develop,  under  the  constant 
head  of  water,  into  a  disastrous  breach. 

There  is  another  respect  in  which  liberality  of  design  is 
advisable  in  works  which  have  to  pass  drainage  discharges. 
The  waterway  provided  should  be  at  least  sufficient  to  pass  the 
maximum  flood  safely.  But  it  is  not  always  easy  to  determine 
even  approximately  what  the  maximum  flood  may  amount  to. 
The  case  of  the  first  Nadrai  aqueduct,  which  was  carried  away 
by  a  flood  of  six  times  the  volume  which  the  design  had 
contemplated,  has  already  been  used  in  Chapter  V.  as  an  illus- 
tration of  the  difficulty  of  calculating  discharges  from  catch- 
ments. There  is  another  instance  of  a  serious  under-estimate 
of  the  maximum  discharge  of  a  drainage  channel  on  which  a 
design  was  based.  A  hill  torrent,  with  a  catchment  area  of 
172  square  miles,  passes  underneath  the  Thapangaing  aqueduct 
in  Burma.  The  original  estimate  of  the  maximum  flood  was 
5,347  cubic  feet  a  second;  a  later  calculation  increased  the 
figure  to  17,760  cubic  feet  a  second.  The  Inspector-General 
of  Irrigation  ruled  that  the  work  should  be  designed  to  pass  a 
flood  of  24,000  cubic  feet  a  second.  The  work  was  designed 
accordingly  and  put  in  hand.  While  it  was  under  construction 
the  Thapangaing  river  rose  20  feet  in  five  hours,  dis- 
charging 56,273  cubic  feet  a  second.  Since  the  design  provided 
waterway  for  less  than  half  this  discharge,  the  work  had  to  be 
modified  and  allowance  made  for  a  discharge  of  60,000  cubic 
feet  a  second.  As  the  aqueduct  was  partly  built,  it  was 
desirable  to  adhere  to  the  original  design  as  far  as  possible. 
The  design  was,  therefore,  altered  so  as  to  provide  for  passing 
the  drainage  discharge  partly  under  the  aqueduct  carrying  the 
canal  and  partly  across  it,  so  that  the  work  has  become  a 
combination  of  an  aqueduct  and  a  level  crossing. 

A  level  crossing  is  controlled  by  three  regulating  works, 
namely,  an  inlet  to  admit  the  drainage  discharge  into  the 
canal,  an  escape  opposite  the  inlet  to  pass  it  out  again,  and  a 
regulator  on  the  canal  down  stream  of  the  level  crossing  to 


MASONRY    WORKS   ON    IRRIGATION   CANALS.  2O/ 

provide  against  fluctuations  of  the  canal  supply,  which  might 
otherwise  be  occasioned  by  the  passage  of  the  drainage  water 
across  the  canal.  The  discharge  passed  across  in  this  way  is 
sometimes  considerable.  The  Rutmoo  torrent,  for  example, 
which  is  carried  across  the  Ganges  Canal  by  a  level  crossing, 
has  a  discharge  of  about  30,000  cubic  feet  a  second. 

In  the  United  States  wood  has  been  much  used  in  the  con- 
struction of  aqueducts.  The  wooden  channels  are  called 
"  flumes,"  a  term  commonly  employed  for  wooden  structures 
which  carry  the  water  of  a  canal  either  round  steep  rocky 
hillsides  or  across  drainage  lines.  But  these  wooden  irrigation 
works  belong  to  a  pioneer  stage.  Not  many  years  hence  they 
will  be  obsolete,  and,  like  wooden  battle-ships  that  have  done 
good  service  in  their  day,  they  will  be  regarded  as  interesting 
survivals  of  an  old  order  that  is  past.  Wood  will  be  replaced 
by  the  more  durable  materials  masonry  and  iron.  There  are 
some  remarkable  instances,  in  the  west  of  the  States,  of  flumes 
constructed  on  a  steep  hillside  to  save  the  cost  of  excavation. 
They  are  known  as  "  bench  "  flumes.  The  bench  flume  on  the 
High  Line  Canal  in  Colorado  is  over  half  a  mile  in  length,  with 
a  cross-section  25  feet  wide  and  7  feet  deep.  Its  discharge  is 
1,184  cubic  feet  a  second.  The  San  Diego  flume  in  California 
is  36  miles  long,  which  is  the  entire  length  of  the  canal,  so 
built  to  avoid  loss  by  absorption.1  Some  remarkable  syphons 
have  also  been  made  of  wood. 

For  aqueducts  of  small  dimensions  iron  is  a  convenient 
material  to  use.  To  prevent  leakage  between  the  ends  of  the 
iron  channel  and  the  masonry  of  the  abutments,  a  junction 
must  be  made  which  will  have  play  enough  to  allow  of  the 
expansion  and  contraction  of  the  iron.  One  way  of  doing  this 
is  to  give  the  ends  of  the  aqueduct  a  bearing  on  a  cushion  of 
felt  soaked  in  tallow,  which  is  let  into  the  stone  of  the  abut- 
ment. This  is  a  security  against  a  leak  along  the  bed. 
The  sides  also  require  staunching.  To  provide  for  this,  lead 
1  ••  Manual  of  Irrigation  Engineering,"  by  Wilson,  p.  258. 


208  IRRIGATION. 

sheeting  is  attached  to  the  iron  of  the  aqueduct  along  the  bed 
and  up  the  sides,  and  grooves  in  the  masonry  made  to  receive 
the  projecting  outer  ends  of  the  lead.  The  grooves  are  then 
filled  up  round  the  lead  with  a  mixture  of  tar,  pitch  and  sand 
poured  in  hot. 

If,  when  canal  and  natural  stream  are  about  the  same  level, 
it  is  not  convenient  for  any  reason  to  resort  to  a  level  crossing 
as  the  means  of  passage,  a  syphon  must  be  substituted  either 
to  carry  the  canal  under  the  stream  or  the  stream  under 
the  canal.  In  the  latter  case  the  work  is  sometimes  called 
a  syphon  aqueduct ;  in  the  former  it  might  consistently  be 
called  a  syphon  superpassage.  In  the  irrigation  literature  of 
the  United  States  a  syphon  is  usually,  with  more  technical 
accuracy,  designated  an  "  inverted  siphon." 

The  design  of  a  masonry  syphon  is  affected  by  the  following 
considerations.  As  it  has  to  pass  below  the  channel  of  an 
upper  watercourse,  its  foundations  generally  descend  to  a 
considerable  depth  below  the  land  surface.  The  deeper  they 
go,  the  more  trouble  may  be  expected  from  springs  over  the 
foundation  bed  during  construction.  The  designer  bears  this 
in  mind,  and  gives  the  barrels  of  his  syphon  width  in  preference 
to  height.  But  a  syphon  is  subject  to  upward  pressure  against 
the  roofing  of  the  barrels,  due  to  the  head  of  water  under  which 
the  syphon  may  be  working.  To  resist  this  and  prevent  the 
pressure  from  lifting  the  crown  of  the  syphon,  there  is  the  com- 
bined weight  of  the  masonry  and  of  whatever  water  'there  may 
be  in  the  channel  over  the  syphon.  As  it  is  possible  that  the 
upper  channel  may  be  dry  when  the  syphon  is  working  under  its 
maximum  head,  this  unfavourable  condition  must  be  assumed 
as  the  basis  of  design,  and  such  a  thickness  of  masonry  be  given 
over  the  syphon  that  its  weight  may  be  sufficient  to  overcome 
the  upward  pressure  of  the  water.  There  are  many  instances  of 
syphons  blowing  up  in  consequence  of  the  water  pressure  exceed- 
ing the  weight  of  the  overhead  masonry.  There  are,  however, 
syphons  in  existence  which  hold  together,  although  the  weight 


MASONRY  WORKS  ON    IRRIGATION   CANALS. 


209 


of  masonry  over  the  barrels  is  insufficient  by  itself  to  resist  the 
water  pressure.  These  owe  their  continued  existence  to  the 
fact  that  the  tensile  strength  of  masonry  joins  forces  with  the 
weight  of  material  in  opposing  the  lifting  force.  But,  in  design- 
ing, it  is  advisable  to  provide  sufficient  weight  above  the  syphon 
vents  to  give  security  without  taking  the  strength  of  the  mortar 
joints  into  account.  The  thickness  of  masonry  that  it  is  on  this 
account  necessary  to  provide  over  the  syphon  affects  the  depth 
to  which  the  foundations  must  be  carried.  The  ordinary  rule 
SUPERPASSAGE 

ON    THE     NIRA    CANAL     INDIA 

Scale 

10    6      0  10  2,0          80          40          60 

fnntmil         I         I        I         I  Feet 

,    /  FIG     C\ 


H\H.W.L. 


SECTION     ALONG     AXIS    OF     BAKKEL 

of  thumb  is  to  make  the  thickness  of  the  crown  of  a  syphon 
equal  to  four-tenths  of  the  maximum  head. 

Various  devices  have  been  resorted  to  with  the  view  of 
reducing  the  deptn  of  the  foundation  bed.  On  the  Nira  Canal 
in  India  a  peculiar  type  of  syphon  has  been  adopted  which  makes 
use  of  the  principle  of  the  arch  to  resist  the  upward  pressure. 
The  syphon  in  longitudinal  section  is  given  the  form  of  an  arch, 
so  that  the  weight  of  the  outer  ends  is  utilised  to  resist  the 
upward  pressure  in  the  tubes,  and  the  syphon  roof  may  be  conse- 
quently lightened.  Fig.  61  gives  a  sketch  of  this  arrangement. 

Another  device  is  the  ingenious  one  designed1  for  the  Ravi 

1  The  construction  of  this  syphon  has  been  abandoned  and  a  "  level- 
crossing  "  substituted. 


210 


IRRIGATION. 


syphon  in  India.  The  diagram  Fig.  62  will  best  explain  the 
principle  of  construction.  Iron  straps  under  the  inverts  below 
the  vents  are  connected  by  iron  vertical  ties  with  horizontal 
girders  above.  Between  the  girders  an  upper  row  of  inverts 
transmits  the  upward  pressure  to  the  girders,  which  cannot 
move  without  lifting  with  them  the  lower  inverts  and  super- 
incumbent masonry.  The  weight  of  the  inferior  masonry  is  thus 
utilised  to  resist  the  water  pressure,  and,  therefore,  the  thickness 
above  the  vents  can  be  reduced. 


FIG     62 


RAVI     SYPHON     INDIA 

PART     CROSS     SECTION 

/ 

i  0  I  2  3  4  s  10  30 

Scale  of  lilil  IMIf        r-f- f—    -4" 


60 
1    Feel 


^ t    fKO.V     BARS 

2  x  |  at  b  intervals 


at  5  intervals 


There  are  two  forms  of  syphon  which  are  common.  In  the 
one  the  tube  is  horizontal  throughout,  and  the  entry  and  exit 
of  the  water  take  place  over  the  sills  of  a  vertical  breast  wall, 
as  in  the  sketch  Fig.  63.  In  the  other  form,  the  ends  of  the 
tube  are  sloped  to  effect  the  change  of  level  between  the 
syphon  waterway  and  the  channel  on  either  side  of  it,  as  in 
the  sketch  Fig.  64. 

The  area  of  waterway  to  be  allowed  in  a  syphon  depends 
upon  the  head  under  which  it  will  work  and  the  consequent 
velocity  of  flow.  If  a  head  sufficient  to  produce  a  velocity  of 
trora  5  to  8  feet  a  second  is  permissible,  the  syphon  should  be 


MASONRY  WORKS  ON    IRRIGATION   CANALS. 


211 


given  a  waterway  which  will  pass  the  maximum  discharge  at 
that  rate  of  flow.  It  is  advantageous  to  obtain  a  high  velocity 
of  flow  in  a  syphon,  inasmuch  as  it  keeps  the  barrel  free 
of  deposit. 

To  avoid  the  difficulty  of  deep  foundations,  syphons  are  often 
made  of  steel  tubes,  bedded,  as  a  rule,  on  concrete,  and  some- 

KAO    NULLAH    SYPHQN    INDIA 

Scale.  FIG     63 

-y-y- 1   i  r  i   i  i- 


100 

I     Feet 


OP    Of    BANK 


W.L.      IN         80NE         CANAL 


SYPHON    ON    CHENAB    CANAL 


Scale 


10      0      10 


0  ,10  60  1 

'  '  ',  '  i,  '  '  '  '  - 


£—100    /0-105—     > 
W.'L.     IN        CANAL 


feef 
FIG 


times  encased  in  it.  If,  however,  the  concrete  casing  is  not  strong 
enough  alone  to  act  as  the  syphon  barrel  when  the  metal 
perishes,  there  is  not  much  gained  by  adding  it  to  the  tube.  If, 
on  the  other  hand,  it  is  strong  enough,  the  internal  tube  might 
as  well  be  omitted  in  the  first  instance.  Even  the  concrete 
bed  is  sometimes  omitted.  A  pipe  syphon  without  any  concrete 
can  be  laid  in  a  flowing  canal  in  the  manner  described  at  the 
end  of  Chapter  VII. 


P  3 


CHAPTER  X. 

METHODS   OF   DISTRIBUTION   OF    WATER,   ASSESSMENT   OF 
RATES,   AND   ADMINISTRATION. 

WHEN  the  means  of  distributing  water  have  been  provided 
in  the  form  of  canals  with  a  complete  system  of  regulating 
works,  the  problem  of  distribution  is  not  thereby  wholly  solved. 
The  method  of  distributing  water  from  a  canal  system  is  almost 
as  important  a  matter  as  the  design  of  the  works  of  distribution. 
The  full  "  duty  "  can  only  be  got  out  of  a  given  quantity  of 
water  by  the  application  of  methods  best  adapted  to  the  condi- 
tions that  prevail  in  any  particular  case.  The  subject  of  water 
"  duty  "  has  already  been  dealt  with  in  Chapter  III.,  and  the 
influence  of  methods  of  distribution  on  the  designing  of  canals 
has  been  referred  to  in  Chapter  VIII. 

If  the  supply  of  water  in  the  main  source  is  greater  than  the 
demand,  as  measured  by  the  needs  of  the  crops  to  be  irrigated, 
the  main  canals  will  be  given  the  necessary  discharge  to  meet 
the  demand.  What  the  discharge  should  be  is  determined  by 
the  actual  area  of  crop  and  the  accepted  " duty"  of  water  for 
that  crop  on  the  particular  canal  under  consideration.  If,  on 
the  other  hand,  the  supply  of  water  is  less  than  the  demand, 
one  of  two  things  must  be  done  ;  either  the  area  of  crop  must 
be  limited  to  that  which  the  available  supply  is  capable  of 
irrigating  with  the  accepted  "  duty  "  of  water  as  the  basis 
of  the  calculation  of  the  area  irrigable,  or  else  the  demand 
must  be  met  by  making  the  water  irrigate  a  larger  area  than 
the  accepted  "  duty "  provides  for.  But  in  the  latter  case, 
since  the  area  of  crop  matured  will  be  larger,  each  acre  of  it 
will  receive  less  water,  or,  in  other  words,  waterings  at  longer 


METHODS  OF   DISTRIBUTION   OF   WATER.  213 

intervals  apart,  than  the  accepted  "  duty  "  assumes  to  be  most 
conducive  to  the  well-being  of  the  crop.  An  example  will  be 
given  later  on  of  the  adoption  of  the  latter  alternative  in  actual 
practice.  If  there  are  several  main  canals  drawing  from  a 
source  of  supply  which  is  inadequate  to  meet  the  demand,  and 
if  all  the  lands  have  equal  claims  to  the  water,  the  partition  of 
the  supply  would  in  fairness  be  made  in  proportion  to  the 
respective  areas  commanded  by  the  canal  systems  on  which 
the  lands  depend  for  their  irrigation.  Each  system  would  thus 
get  its  fair  share  of  the  available  supply,  and  the  question  as 
to  whether  the  crop  area  should  be  limited,  or  a  reduced  quantity 
of  water  per  acre  be  allowed,  could  be  settled  for  each  system 
independently  of  the  others  as  might  seem  best. 

When  there  is  a  sufficiency  of  water  to  satisfy  everybody, 
each  individual  cultivator  might  be  allowed  to  help  himself  if 
the  water  were  to  be  given  without  price.  But,  even  if  there 
be  a  sufficiency,  the  water  supplied  has  to  be  paid  for  in  some 
form  or  another.  The  water  rate  may  be  levied  on  the  area  of 
crop  either  brought  to  maturity  by  irrigation,  or  given  a  singie 
watering,  or  irrigated  for  certain  months.  The  cultivators  pay 
an  amount  proportional  to  the  area  of  crop  irrigated  and 
dependent  on  the  nature  of  the  crop,  some  crops  requiring 
more  water  than  others  to  bring  them  to  maturity.  The 
watered  field  and  the  standing  crop  furnish  the  data  required 
for  calculating  the  amount  due  from  the  cultivator.  The 
objection  to  such  a  mode  of  assessment  is  that  the  cultivator 
has  no  inducement  held  out  to  him  to  economise  water. 

The  other  method  of  assessment  is  to  charge  the  water  rate 
on  the  actual  quantity  of  water  used.  This  method  requires 
some  means  of  measuring  the  water.  Different  forms  of  water 
meters,  or  modules,  have  been  invented  for  the  purpose ;  but 
the  conditions  of  flow  in  open  irrigation  channels  do  not  lend 
themselves  to  the  accuracy  of  measurement  which  is  attainable 
with  water  meters  in  pipes  flowing  under  considerable  pressure, 
as  in  the  case  of  a  city  supply  system.  Some  of  the  modules 


214  IRRIGATION 

devised  are  ingenious,  but  they  are  only  suitable  for  small 
discharges  and  for  use  in  countries,  such  as  Italy,  where  the 
ethics  of  irrigation  have  reached  such  an  advanced  stage  of 
evolution  that  "  it  is  thought  apparently  as  discreditable  to 
appropriate  an  unfair  supply  of  water  as  to  steal  a  neighbour's 
horse,  as  discreditable  to  tamper  with  the  lock  of  the  water 
module  as  with  the  lock  of  a  neighbour's  barn."  l 

When  the  supply  of  water  is  not  in  excess  of  the  demand,  an 
economical  and  just  distribution  depends  more  on  correct 
methods  of  administration  than  on  the  perfection  and  complete- 
ness of  the  regulating  works.  All  countries  that  have  practised 
irrigation  on  a  large  scale  have  found  it  necessary  to  adopt 
some  system  of  "  rotation "  whereby  water  is  alternately 
supplied  and  withheld  for  fixed  periods.  Under  this  system 
the  total  area  requiring  irrigation  is  divided  up  into  two  or 
more  sections,  and  each  section  in  succession  is  given 
water,  while  at  the  same  time  it  is  withheld  from  the  other 
sections.  The  duration  of  the  period  of  supply  is  propor- 
tional to  the  area  of  crop  included  in  the  section  whose 
turn  it  is  to  be  watered.  The  more  perfect  are  the 
methods  of  administration  and  the  means  of  regulation,  the 
more  minute  can  be  the  subdivision  into  sections,  and 
the  more  exact  will  be  the  just  distribution  of  water.  But 
there  are  practical  considerations  which  impose  a  limit  on 
the  subdivision.  The  operation  of  irrigating  a  single  acre 
takes  a  certain  time,  say  two  hours,  and  requires  a  certain 
discharge,  say  2j  cubic  feet  a  second,  to  complete  the  watering. 
Theoretically  «  double  the  discharge  should  complete  the 
irrigation  of  the  acre  in  one  hour,  but  practically  the  cultivator 
would  find  that  he  could  not  lead  the  water  about  his  field  at 
the  pace  required  to  complete  its  irrigation  in  this  short  time. 
As  a  rule,  the  subdivision  does  not  go  so  far  as  to  create 
sections  of  so  small  an  area  as  a  few  acres ;  but  in  Italy,  for 
instance,  where  distribution  of  water  is  carried  out  in  a  more 

1  Colonel  Sir  C.  Scott- Moncrieffs  address,  British  Association,  1905. 


METHODS   OF   DISTRIBUTION   OF   WATER.  215 

perfect  manner  than  in  any  other  country,  the  sections  are  so 
small  that  the  duration  of  the  supply  periods  is  reckoned  by  hours, 
and  not  by  days.  Each  cultivator  is  allowed  the  use  of  the  water 
for  a  number  of  hours  proportional  to  the  area  of  his  crop,  and 
pays,  according  to  the  area  he  waters,  his  contribution  towards 
the  total  cost  of  the  maintenance  of  the  irrigation  system,  and 
his  share  of  the  sum  which  has  to  be  paid  to  the  Government. 

In  France  also  the  rotation  periods  are  measured  in  hours. 
Whatever  the  area  may  be,  water  is  supplied  to  cultivators  at  a 
constant  discharge  of  30  litres  (ro6  cubic  feet)  per  second. 
The  period  of  flow  allowed  is  reckoned  at  the  rate  of  five  hours 
per  hectare  (two  hours  per  acre).  As  the  land  is  much  subdivided 
and  the  irrigation  has  to  be  continued  by  night  as  well  as  by 
day,  the  rotation  programme  is  so  drawn  up  that  the  same 
people  may  not  always  get  their  turn  during  the  night.  This 
is  arranged  for  by  making  the  interval  between  waterings  so 
many  whole  days  and  a  fraction  of  a  day,  the  odd  hours  being 
introduced  for  a  similar  purpose  to  the  dog-watch  on  a  ship. 
The  intervals  between  waterings,  in  the  case  of  land  devoted 
to  market  gardening,  are  from  six  to  seven  days.  The  irrigation 
season  lasts  about  six  months,  so  that  about  thirty  waterings  are 
given  to  the  irrigated  lands.  With  intervals  between  waterings 
of  six  and  a  half  days,  and  allowing  five  hours  per  hectare,  a 
discharge  of  30  litres  (ro6  cubic  feet)  per  second  would  irrigate 
an  area  of  30  hectares  (74  acres)  of  crop.  The  allowance 
made  provides  a  volume  equivalent  to  a  depth  of  2j  inches 
over  the  whole  area  irrigated  for  each  separate  watering. 

In  Spain  also  the  distribution  periods  are  sometimes  measured 
in  hours.  The  irrigated  lands  of  the  Henares  valley,  for  example, 
are  divided  into  plots  of  about  800  acres.  Each  plot  is  served 
by  a  branch  canal  taking  off  from  the  main  canal.  The  branch 
canal  is  fed  through  a  module,  a  continuous  discharge  at  the 
rate  of  T  cubic  foot  a  second  for  every  156  acres  being  allowed. 
The  fields  are  irrigated  by  a  number  of  distributaries  taking  off 
from  the  branch  canal.  The  whole  discharge  of  the  branch 


2l6  IRRIGATION. 

canal  is  turned  into  each  distributary  in  succession,  and  each 
individual  landlord  or  tenant  is  given  the  water  for  a  period, 
measured  in  hours  and  minutes,  proportional  to  the  area  of  the 
crop  on  his  holding.  In  this  way  each  separate  holding  gets  a 
watering  at  regular  intervals. 

In  India  the  rotation  system,  copied  from  Europe,  is  known 
among  the  natives  as  irrigation  by  tatils  ;  Egypt  copied  it  from 
India,  and  the  fellah  calls  it  irrigation  by  manawabah ;  in 
Java,  where  also  it  is  practised,  it  is  called  the  golongan  system, 
all  these  expressions  signifying  irrigation  by  turns. 

The  advantages  of  such  a  system  are  many.  By  concen- 
trating the  available  supply  in  half,  or  a  third,  or  a  less  fraction 
of  the  canals,  and  giving  the  whole  of  it  to  the  section  whose 
turn  it  is  to  take  water,  the  irrigation  is  made  easy  in  conse- 
quence of  the  higher  water  levels  produced  in  the  canals.  At 
the  same  time,  in  the  other  sections  which  are  not  receiving 
water,  the  danger  of  the  canals  causing  waterlogging  of  the  soil 
is  removed,  as  they  are  either  empty  or  flowing  at  a  low  level. 
The  crops  require  water  at  certain  intervals,  and  not  con- 
tinuously. It  is  better  for  them,  as  soon  as  they  have  received 
a  watering,  that  the  water  supply  should  be  shut  off  from  their 
neighbourhood,  so  that  all  excess  of  water,  over  and  above  that 
used  up  or  absorbed,  may  be  got  rid  of,  and  not  be  allowed  to 
stagnate.  Irrigation  by  rotation,  moreover,  is  a  system  that 
conduces  to  economy  of  water.  For  the  water  is  delivered  just 
where  and  when  it  is  wanted  for  irrigation,  and  is  therefore  not 
allowed  to  run  to  waste.  The  loss  from  evaporation  and 
absorption  is  less,  as  the  water  is  spread  out  over  a  less  extent 
of  canals.  The  irrigation  staff  can  superintend  the  distribution 
more  thoroughly,  as  their  exertions  can  be  wholly  devoted  to 
the  section  under  irrigation  for  the  period  of  its  supply.  The 
cultivators  also  find  such  an  arrangement  a  convenience,  as 
they  know  exactly  when  they  must  arrange  to  water  their  fields. 
Moreover,  the  velocity  of  current  of  the  canals,  when  in  flow, 
is  maintained  at  a  high  rate  in  consequence  of  the  fuller 


METHODS  OF   DISTRIBUTION   OF   WATER.  217 

discharge,  whereby  more  of  the  silt  is  carried  forward  to  the 
fields  and  less  deposited  in  the  canal.  Lastly,  the  system 
ensures  an  equitable  distribution  of  the  water  to  all  cultivators, 
and  offers  such  facilities  for  reducing  the  amount  of  waterings 
given  in  a  season  of  short  supply  that  the  drawbacks  of  a 
deficient  supply  can  be  made  to  bear  equally  on  all,  with  a 
minimum  of  disadvantage  to  anyone. 

In  India  there  are  two  modes  of  applying  the  rotation 
system.  One  arrangement  is  that  in  which  all  the  distributing 
canals  are  kept  in  continuous  flow,  and  the  outlets,  supplying 
the  village  channels,  are  opened  and  closed  by  turns.  The 
outlets  are  grouped  into  two  or  more  sections,  and  each  section 
is  allowed  to  take  water  for  a  certain  number  of  days  in  its 
proper  turn.  The  other  and  better  arrangement  is  that  in 
which  the  distributaries  are  subjected  to  rotation.  As  with  the 
outlets,  they  are  grouped  into  sections,  and  each  section  in  turn 
flows  with  full  discharge  while  the  others  are  closed.  Sometimes 
a  combination  of  these  two  arrangements  is  adopted,  and  rota- 
tions are  applied  to  groups  of  distributaries,  and  again  to  groups 
of  outlets  on  those  distributaries.  "  In  the  simplest  cases, 
where  only  the  outlets  from  the  distributaries  are  tatiled,  it  is 
usual  to  divide  the  distributary  into  three  lengths,  so  that  the 
village  channels  taking  off  each  length  command  areas  which  are 
approximately  equal.  The  outlets  in  the  first  length  of  the 
distributary  usually  get  water  for  three  days  in  each  week,  and 
are  closed  for  four  days.  The  outlets  in  the  second  length  of 
distributary  are  open  on  the  four  days  when  those  in  the  first 
length  are  closed,  and  closed  on  the  three  days  when  the  others 
are  open  ;  in  the  third  length  of  the  distributary  the  outlets  to 
the  village  channels  are  allowed  to  be  open  all  the  week  as  a 
rule,  and  they  absorb  all  the  water  passed  on  by  the  upper 
lengths"  (Buckley). 

When  the  distributaries  are  subject  to  rotation,  the  pro- 
gramme has  to  be  drawn  up  to  cover  longer  periods,  and  it 
becomes  more  complicated.  The  recent  history  of  irrigation 


2l8  IRRIGATION. 

in  Egypt  furnishes  a  good  example  of  this  alternative  method 
of  applying  the  rotation  system. 

In  Egypt  the  severest  application  of  the  system  of  irrigation 
by  turns  was  made  in  the  summer  of  1900,  when  the  scantiness 
of  the  available  water  supply,  in  relation  to  the  requirements 
of  the  cultivated  area,  exceeded  all  previous  and  subsequent 
experience.  The  irrigation  officers  were  faced  with  this 
problem.  There  was  a  certain  area  of  land  under  cotton 
which  had  to  be  irrigated ;  there  was  an  insufficient  and  con- 
stantly diminishing  supply  with  which  to  irrigate  it.  The 
Assuan  reservoir  was  not  as  yet  in  existence.  The  crop,  that 
was  in  danger  of  suffering  for  want  of  timely  irrigation,  was 
cotton,  on  which  the  wealth  of  modern  Egypt  principally 
depends.  The  cotton  plant,  during  the  season  of  low  supply 
in  summer,  requires  watering  at  intervals  of  eighteen  days.  It  is 
generally  believed  that  the  yield  is  diminished  if  the  intervals 
between  waterings  are  prolonged  beyond  eighteen  days.  But,  in 
the  summer  of  1900,  there  was  not  enough  water  in  the  river  to 
complete  one  watering  of  the  whole  cropped  area  in  so  short  a 
period.  There  were  then  only  two  possible  alternatives  to 
choose  between  :  either  the  area  of  crop  to  be  irrigated  must  be 
reduced  to  that  which  the  discharge  was  capable  of  watering  in 
eighteen  days,  or  a  longer  time  for  the  watering  must  be  allowed. 
The  practical  impossibility  of  reducing  the  crop  area,  once  it 
had  been  planted,  without  doing  injustice  to  individuals,  caused 
the  rejection  of  this  alternative.  It,  therefore,  remained  to 
arrange  a  programme  by  which  sufficient  time  should  be  allowed 
for  the  irrigation  of  the  whole  area  of  cotton  crop.  A  given 
discharge  takes  a  definite  time  to  irrigate  a  given  area,  and,  as 
the  discharge  decreases,  the  time  of  the  operation  must  increase; 
that  is,  in  other  words,  the  intervals  between  the  waterings  of 
any  particular  field  must  be  longer.  It  was  found  a  convenient 
arrangement  to  divide  each  separate  system  of  canals  into  three 
sections,  which  were  designated  A,  B,  and  C.  Now  much  of 
the  irrigation  was  effected  by  pumps,  which,  it  was  calculated, 


METHODS  OF   DISTRIBUTION   OF   WATER.    . 


219 


could  complete  the  irrigation  of  all  the  crops  depending  on  them 
in  six  days,  but  not  in  less.  So  six  days  was  accepted  as  the 
period  of  working  for  each  section.  If  the  water  supply  had  been 
sufficient  to  irrigate  the  whole  cropped  area  in  eighteen  days, 
each  section  would  have  taken  water  in  turn  for  six  days,  and  have 
been  prevented  from  taking  it  for  the  succeeding  twelve  days ; 
that  is,  the  interval  between  waterings  for  any  particular  field 
would  have  been  eighteen  days.  But  it  was  found  that  the  supply 
was  only  sufficient  at  first  to  give  one  watering  in  twenty  days, 
and  later  on  in  twenty-four  days,  and  still  later,  at  lowest  supply, 
in  twenty-eight  days.  To  arrange  for  the  twenty-eight  days' 
rotation,  it  was  necessary  to  rearrange  the  subdivision  and  to 
group  the  canals  into  four  sections,  which  were  called  D,  E,  F, 
and  G,  to  avoid  confusion  with  the  threefold  arrangement. 
The  programmes  of  rotation  were,  then,  made  out  on  the 
following  basis : — 


Three  Sections. 


One  watering  One  watering 
in  20  days.        in  24  da>  s. 


Section  A  takes  water 

6  days 

6  days 

B  and  C  stop. 

General  stoppage 

i 

2      ,, 

Section  B  takes  water 

6 

6     „ 

A  and  C  stop. 

General  stoppage 

i 

2      „ 

Section  C  takes  water 

6 

6     „ 

A  and  B  stop. 

General  stoppage 

•• 

2      „ 

20  days 

24  days 

Four  Sections. 

One  watering  in  28  days. 

Section 

D  takes  water 

6  days 

E,  F, 

and 

G 

stop. 

General 

stoppage    . 

i 

Section 

E  takes  water 

6 

D,  F, 

and 

G 

stop. 

Genera] 

stoppage    . 

i 

Section 

F  takes  water 

6 

D,  E, 

and 

G 

stop. 

Genera] 

stoppage     . 

* 

Section 

G  takes  water 

6 

D,  E, 

and 

F 

stop. 

General 

stoppage    . 

i 

28  days 

2?Q  IRRIGATION. 

The  general  stoppages  of  one  or  two  days  were  intended  to 
provide  for  the  filling  of  the  channels  of  the  section  whose  turn 
to  work  came  next,  so  that  the  water  might  reach  the  tail  ends  of 
the  sections,  and  the  pumps  at  the  tails  have  as  good  a  supply 
from  the  commencement  of  their  six-days  period  as  those  higher 
up  the  canals.  These  intermediate  general  stoppage  days  were 
also  used  to  give  water  to  those  who  had  been  badly  supplied 
during  their  proper  working  period.  It  was  moreover  arranged 
that,  if  the  tail  reaches  of  any  section  did  not  get  water  in  their 
proper  turn,  they  should  be  given  water  with  the  section  whose 
turn  came  next.  By  so  arranging,  it  became  possible  to  get 
water  to  them,  since  all  the  pumps  or  heads  above  them  on  the 
same  branch  were  stopped.  The  intermediate  days  of  general 
stoppage  provided  a  reserve  which  could  be  utilised  to  prevent 
arrears  accumulating  to  such  an  extent  as  to  upset  the  published 
programmes  and  introduce  confusion  during  the  most  critical 
period. 

In  the  summer  of  1900,  in  Egypt,  the  supply  was  so  short 
that,  if  the  cotton  crop  was  to  be  saved,  provision  could  not  be 
made  for  rice  irrigation,  and  as  the  rice  crop  in  comparison 
with  the  cotton  crop  was  of  little  importance  in  both  extent 
and  value,  it  was  sacrificed  to  the  needs  of  the  more  valuable 
crop.  By  such  measures  as  described,  the  cotton  crop  was 
irrigated  by  a  discharge  of  21  cubic  metres  a  day  per  acre, 
instead  of  the  normal  30  cubic  metres  a  day  which  is  the 
discharge  required  to  allow  for  waterings  being  given  every 
eighteen  days.  The  latter  is  the  "  accepted  duty,"  as  has  been 
explained  in  Chapter  III.;  the  former  represents  the  actual  work 
done  by  the  water  in  the  summer  of  1900.  According  to  the 
accepted  "duty,"  i  cubic  foot  a  second  should  irrigate  8iJ  acres; 
in  the  summer  of  1900,  i  cubic  foot  a  second  was  made  to  irrigate 
116  acres,  or  more  than  42  per  cent,  in  excess  of  the  "  accepted 
duty."  "  But,  under  these  circumstances,  some  of  the  crop 
suffered  in  yield  from  insufficiency  of  water,  and  so  the  season's 
apparent  "duty"  included  duty  imperfectly  performed  in 


METHODS  OF   DISTRIBUTION   OF   WATER.  221 

consequence  of  the  water  having  been  called  upon  to  do  work 
beyond  its  powers. 

After   the  experience  of  a   succession   of  low   summers   in 

Egypt,  the  conclusions  arrived  at,  as  to  the  best  programme  for 

rotations,  is  thus  stated  in  the  Irrigation  Report  of  Egypt  for 

1902  : — "  As  a  consequence  of  previous  experience,  it  has  been 

decided  in   1903  to   adopt   the   three-section   arrangement   of 

distribution,  by  which  each  section  takes  water  in  turn  for  a 

third  of  a  full  period,  which  has  been  fixed  at  eighteen  days ;  so 

that  each  section  will  get  water  for  six  days,  and  be  without  it 

for  twelve.     For  canals,  however,  from  which  rice  is  irrigated, 

two  sections  are  adopted,  each  section  working  for  four  days  and 

stopping  for  five.      The  day  when  neither  section  works  comes 

after  the  working  of  the  first  section,  and  is  utilised  for  filling 

the  channels  of  the  second  section  before  water  is  drawn  oft 

from  them.     As  the  rice  full  period  is  half  of  the  cotton  period, 

a   cultivator   may,    if  he   likes,    raise  cotton  or  rice,  or  both. 

Supposing   he   has   an   area   of  200  acres  to  put  under  crop, 

he  can  put  it  all  under  rice  and  irrigate  it  once  in  nine  days ; 

or    he   can   put   it   all   under   cotton   and   irrigate   100   acres 

during  one  turn  and  100  acres  during  the  next,  so  that  one 

watering  in  eighteen  days  is  given  to  it  all.     Or  he  may  put 

100  acres  under  rice  and  100  under  cotton.     In  this  case  he 

would  irrigate  all  the  rice  and  50  acres  of  cotton  during  one 

turn  ;  and  all  the  rice  again  and  the  other  50  acres  of  cotton 

the   next  turn  :    so  that,  in  every  case  the  rice  would  get  a 

watering  in  nine  days,  and  the  cotton  in  eighteen  days.     The 

cultivator  is  thus  free  to  plant  what  he  likes." 

This  programme  contemplated  assistance  from  the  Assuan 
reservoir,  which  had  been  completed  in  1902.  Without  such 
assistance,  the  period  of  eighteen  days  would  have  had  to  be 
increased  to  twenty-one,  and  later  to  twenty-four,  days  by 
inserting  one  or  two  days  of  general  stoppage  between  each 
section's  period  of  working,  as  was  done  in  1900.  With  a 
period  of  nine  days  between  waterings  of  rice,  and  of  eighteen 


IRRIGATION. 

days  between  waterings  of  cotton,  the  discharge  required  at  the 
canal  head  was  found  to  be  at  the  rate  of  30  cubic  metres  (1060 
cubic  feet)  a  day  per  acre  of  cotton  crop,  and  at  the  rate  of  60 
cubic  metres  for  rice.  If  the  supply  falls  short  of  these  allow- 
ances, there  are,  as  has  already  been  stated,  only  two  ways  of 
meeting  the  deficiency  of  supply,  namely,  either  by  lengthening 
the  intervals  between  waterings  or  by  reducing  the  area  of 
crop  to  be  watered.  The  former  is  sometimes  the  only 
practicable  alternative. 

If  the  other  alternative  of  reducing  the  area  of  crop  is 
adopted,  the  reduction  must  be  determined  upon  before  the  crop 
is  sown  or  planted.  Sir  Colin  Scott-Moncrieff,  in  his  address 
at  the  Meeting  of  the  British  Association,  1905,  already  quoted, 
thus  describes  the  system  of  distribution  under  the  "  Irrigation 
Association  West  of  the  Sesia,"  in  Italy:  "To  effect  the 
distribution  of  the  water  the  area  irrigated  is  divided  into 
districts,  in  each  of  which  there  is  an  overseer  in  charge  and 
a  staff  of  guards  to  see  to  the  opening  and  closing  of  the 
modules  which  deliver  the  water  into  the  minor  water  courses. 
In  the  November  of  each  year  each  parish  sends  in  to  the 
direction-general  an  indent  of  the  number  of  acres  of  each 
description  of  crop  proposed  to  be  watered  in  the  following 
year.  If  the  water  is  available  the  direction-general  allots  to 
each  parish  the  number  of  modules  necessary  for  this  irrigation  ; 
but  it  may  quite  well  happen  that  the  parish  may  demand 
more  than  can  be  supplied,  and  may  have  to  substitute  a  crop 
like  wheat,  requiring  little  water,  for  rice,  which  requires  a 
great  deal." 

In  certain  districts  of  India  it  is  considered  desirable  to 
restrict  the  area  under  irrigation  to  a  certain  proportion  of  the 
area  commanded.  "  When  the  available  supply  of  water  is 
insufficient  to  irrigate  the  whole  cultivable  area  commanded, 
such  a  restriction  is  desirable  for  the  sake  of  distributing  the 
water  to  as  many  parts  of  the  district  as  possible  for  the 
benefit  of  the  people.  But  there  is  another  reason  for  the 


METHODS   OF   DISTRIBUTION   OF   WATER.  223 

restriction.  If  irrigation  is  spread  over  all  the  area  commanded, 
the  soil,  when  light,  is  liable  to  become  water-logged,  and  the 
spring  levels  may  be  unduly  raised. 

In    the   discussion   on   the    Irrigation    Papers   read   at    the 
International    Engineering   Congress   of   1904,    at    St.   Louis, 
Mr.  J.    E.    de    Meyier   describes   the   system    of  rotation,    or 
golongan  system,  as  practised  in  Demak,  Java:     "The  fields 
are  divided  into  four,  five  or  six  classes :  those  of  the  second 
class  get  the  water  a  week  later  than  those  of  the  first ;  those  of 
the  third  a  fortnight  later,  and  so  on."     Mr.  de  Meyier  gives  the 
following   example   to   explain   the    system,    taking    a    quick 
growing  kind  of  rice  as  the  crop  of  his  illustration.     "  The  rice 
fields  are  under  irrigation  for  nineteen  weeks.     For  the  first 
two  weeks  of  this  period  the  discharge  required  for  the  pre- 
liminary operation  of  ploughing  is  at  the  rate  of  i  cubic  foot  a 
second   for   every   50   acres.     After  the  ploughing  the  rice  is 
sown  on  about  a  tenth  of  the  area  to  form  nurseries  for  the 
seedlings,  which  will  afterwards  be  transplanted  to  cover  the 
whole  area.     The  nursery  period  lasts  five  weeks,  and  during 
this  time  the  discharge  needed  is  at  the  rate  of  i  cubic  foot  a 
second  for  every  50  acres  of  nursery  area,  with  an  addition  of 
i  cubic  foot  for  every  2,000  acres  of  the  whole  area  to  allow  for 
further  tilling  operations.     After  transplanting  the  seedlings  to 
the  larger  area,  an  increased  supply  at  the  rate  of  i  cubic  foot  a 
second  to  every  150  acres  for  a  week,  and  then  at  the  rate  of  i 
cubic  foot  a  second  to  about  every  80  acres  for  three  weeks,  is 
required ;  and  thereafter  a  gradually  diminishing  supply  till  the 
nineteenth  week.     If  then,  for  instance,  the  total  area  of  the 
rice  fields  is  10,000  acres,  and  if  the  whole  of  it  is  taken  in 
hand  at  once,  the  discharges  required  will  be  those  represented 
by  the  figures  of  the  second  column  of  the  accompanying  table. 
Now  supposing  the  river  from  which  the  supply  is  drawn  never 
discharges  more  than   95   cubic   feet   a  second,  and  that   it 
continues  to  flow,  though  with  diminishing  volume,  for,  say, 
twenty-five  weeks,  how  are  the  10,000  acres  of  rice  crop  to  be 


224  IRRIGATION. 

irrigated  under  these  conditions,  seeing  that  for  seven  weeks  out 
of  the  nineteen  a  greater  discharge  than  95  cubic  feet  a  second 
appears,  from  the  figures  in  the  second  column  of  the  table,  to 
be  necessary  ?  The  method  of  solving  the  problem  is  this : 
The  10,000  acres  of  rice  field  are  divided  into  five  sections,  A, 
B,  C,  D,  and  E,  of  2,000  each.  For  the  first  two  weeks 
sections  A  and  B  get  the  full  discharge  required  for  the 
preliminary  operation  of  ploughing,  and  the  other  three  sections 
are  left  alone.  In  the  third  and  fourth  weeks  sections  C  and 
D,  and  in  the  fifth  and  sixth  weeks  section  E,  get  in  their  turn 
the  full  discharge  required.  For  the  five  weeks  succeeding  the 
ploughing,  each  section  successively  gets  the  reduced  supply 
required  for  its  nursery,  and  after  that  an  increase  when  the 
seedlings  are  planted  out,  followed  by  a  decrease  as  the  plant 
becomes  mature.  But  in  sections  D  and  E  the  nursery  stage 
has  to  be  prolonged  to  six  and  seven  weeks  respectively  on 
account  of  the  limited  supply  not  admitting  of  an  increase  at 
the  end  of  five  weeks." 

"The  table  on  the  next  page  shows  this  method  of  over- 
lapping, whereby  it  is  arranged  that  the  total  discharge 
required  at  any  time  never  exceeds  the  river  discharge  of 
95  cubic  feet  a  second.  The  figures  in  the  last  column  give 
the  aggregate  daily  discharges  required  by  the  five  sections, 
week  by  week,  for  the  twenty-five  weeks  of  the  rice-cultivating 
period." 

As  a  contrast  to  systems  of  rotations  which  have  been  devised 
to  do  equal  justice  to  all  concerned,  the  custom  of  " priorities" 
of  the  United  States  is  worth  notice.  The  law  recognises  the 
prior  right  of  first  comers  to  be  first  served  with  the  water  of 
running  streams  to  the  extent  to  which  they  put  it  to  profitable 
use.  The  man  who  first  made  use  of  the  water  of  any  stream 
to  cultivate  a  certain  area  is,  by  custom  and  law,  entitled  to 
withdraw  the  same  quantity  of  water  when  his  land  requires  it, 
without  regard  to  the  interests  of  his  neighbours.  The  man 
who  followed  him,  at  no  matter  what  interval  of  time,  has  a 


METHODS  OF   DISTRIBUTION   OF   WATER. 


225 


secondary  right,  and  may  in  future  withdraw  from  the  stream 
the  amount  of  water  originally  used  to  cultivate  his  farm, 
provided  there  is  sufficient  to  first  supply  the  prior  settler. 
The  man  who  is  third  in  point  of  time  can  utilise  his  share  only 


Number 
of  Week. 

Supply  in  Cubic  Feet  per  Second. 

Aggregate 
Supply 
Required. 

The  whole 
Area  of 
TO,OOO  Acres 
at  ono*. 

The  Area  divided  into  Five  Sections  of  2,000  Acres  each. 

Section 

A. 

B. 

c. 

D. 

£. 

I 

200 

40 

40 

_ 

_ 

_ 

80 

2 

20O 

40 

40 

— 

— 

— 

80 

3 

25 

5 

5 

40 

40 

— 

90 

4 

25 

5 

5 

40 

40 

— 

90 

5 

25 

5 

5 

5 

5 

40 

60 

6 

25 

5 

5 

5 

5 

40 

60 

7 

25 

5 

5 

5 

5 

5 

25 

8 

80 

16 

16 

5 

5 

5 

47 

9 

120 

24 

24 

5 

5 

5 

63 

10 

120 

24 

24 

16 

5 

5 

74 

ii 

I2O 

24 

24 

24 

16 

5 

93 

12 

IOO 

20 

20 

24 

24 

5 

93 

13 

IOO 

20 

20 

24 

24 

5 

93 

14 

75 

15 

15 

20 

24 

16 

90 

15 

75 

15 

15 

20 

20 

24 

94 

16 

50 

10 

IO 

15 

20 

24 

79 

i? 

50 

10 

10 

15 

15 

24 

74 

18 

25 

5 

5 

10 

15 

20 

55 

19 

25 

5 

5 

10 

10 

20 

50 

20 

— 

— 

— 

5 

10 

15 

30 

21 

— 

— 

— 

5 

5 

15 

25 

22 

— 

— 

— 

— 

5 

10 

15 

23 

— 

— 

— 

— 

— 

10 

10 

24 

— 

— 

— 

— 

— 

5 

5 

25 

~ 

" 

~ 

~ 

~ 

5 

5 

after  the  first  and  second  men  have  had  their  prior  claims 
satisfied;  and  so  on,  the  late  comers  being  compelled,  if  neces- 
sary, to  leave  the  water  untouched  until  all  with  prior  rights 
have  had  the  full  quantity  which  is  their  legal  due.  As  the 
country  develops  under  the  stimulus  of  irrigation,  there  is  a 
growing  tendency  to  abandon  the  observance  of  priorities,  and 
I.  Q 


226  IRRIGATION. 

to  adopt  the  principle  of  distribution  according  to  areas  of  crop 
or  cultivated  land. 

When  the  delivery  and  distribution  of  a  water  supply  is 
effected  by  an  artificial  system  of  canals,  it  is  usual  to  charge 
for  the  irrigation  by  water  rates  in  some  form  or  other.  In 
Java,  however,  there  is  no  water  rate  or  charge  for  water.  The 
rainfall  of  the  island  is  considerable,  and  it  would  be  difficult  to 
estimate  to  what  extent  a  full  supply  from  canals  benefits  the 
crops  which  hitherto  had  depended  mostly  on  rain  assisted  by 
a  scanty  allowance  of  irrigation  water.  The  land  tax  is 
assessed  in  relation  to  the  average  yield  of  the  crops  grown, 
which  depends  on  the  fertility  of  the  soil  and  the  nature  of  the 
water  supply.  When  the  water  fails,  a  partial  remission  of  the 
tax  is  allowed.  The  land  tax  assessment  and  collection  thus 
takes  account  of  the  irrigation  supplied,  and  no  additional 
water  rate  can  be  levied. 

In  Egypt  also  there  is  no  Government  water  rate.  Payment 
of  the  land  tax  confers  the  right  to  a  supply  of  water  sufficient 
for  the  maturing  of  one  crop  during  the  year,  and  imposes  on 
the  Government  the  obligation  to  make  that  supply  available. 
If  the  Government  fails  to  do  so,  the  land  tax  is  remitted.  The 
only  measurements  made  are  of  those  areas  which  have 
remained  without  water  throughout  the  year  from  no  fault  of 
the  cultivator,  and  on  which  the  land  tax  has,  therefore,  to  be 
remitted.  The  irrigation  officers  of  Egypt  are  thus  relieved  of 
all  the  troublesome  revenue  work  which  adds  so  much  to  the 
duties  of  the  irrigation  staff  in  India. 

The  rates  charged  in  India  for  the  water  required  to  mature  a 
crop  vary  from  i  rupee  an  acre  for  rice  to  20  rupees  an  acre  for 
sugar-cane.  The  average  rate  for  the  whole  of  India  is  rather  more 
than  3  rupees  an  acre  for  the  revenue  realised,  and  in  addition 
i  rupee  an  acre  for  working  expenses.  Compared  with  the 
value  of  the  crops  raised  by  irrigation  the  water  rates  charged 
in  India,  if  not  low,  are  decidedly  moderate.  But  in  India  as 


METHODS  OF   DISTRIBUTION   OF   WATER.  227 

a  rule  the  crops  are  not  wholly  dependent  on  the  canals,  as,  to 
a  varying  extent,  rainfall  supplies  the  water  needed.  The 
water  rate  may  therefore  be  considered  to  be  made  in  return 
for  a  guarantee  that  sufficient  water  shall  be  supplied  to  ensure 
the  maturing  of  the  crop.  But  in  Sind,  where  crops  are  grown 
only  on  irrigated  land,  and  where  land  without  water  is  value- 
less— the  conditions  being  much  the  same  as  in  Egypt — there 
is  no  separate  charge  for  irrigation.  As  in  Java  and  Egypt,  the 
assessments  of  the  land  revenue  are  made  on  the  basis  of  the 
average  produce,  and  account  is  thus  taken  of  the  increase  of 
yield  due  to  irrigation.  This  system  of  a  "  consolidated  "  rate 
is  followed  also  throughout  the  Madras  Presidency,  in  certain 
districts  of  Burmah,  and  also  in  some  parts  of  Bombay  depend- 
ing on  old  irrigati  on  works. 

In  the  Western  States  of  America,  where  the  rainfall  is  less 
than  20  inches  per  annum,  a  water  rate  is  charged  of  from 
£2  8s.  to  £4  per  acre,  the  farmer  paying  in  addition  a  rate  of 
from  2s.  to  los.  per  acre  annually  for  maintenance.  In 
comparison  with  India  these  rates  appear  high. 

In  Piedmont  in  Italy  the  farmer  pays,  according  to  the  area 
he  waters,  his  share  both  of  the  sum  which  is  due  to  the  govern- 
ment and  of  the  cost  of  maintaining  the  irrigation  works.  The 
Government  charge  per  annum  is  at  the  rate  of  800  liras  per 
module  of  2*047  cubic  feet  per  second  delivery,  or  £15  125.  yd. 
per  cubic  foot  per  second. 

In  France  the  association  or  syndicate  that  manages  the 
canals  charges  a  water  rate  on  the  basis  of  a  continuous  flow 
of  I  litre  per  second  per  hectare.  The  rate  varies  from  35  to 
70  francs  per  annum  per  hectare,  equivalent  to  125.  to  245. 
per  acre. 

In  Spain  the  price  of  water  varies  considerably.  The 
followers  of  the  conquerors  who  expelled  the  Moors  pay- 
nothing  for  the  irrigation  works  that  serve  the  lands  granted 
to  them  in  reward  for  their  services,  excepting  only  a  small 
annual  tax  to  cover  the  cost  of  maintenance.  The  same 

Q  2 


228  IRRIGATION. 

privilege  is  enjoyed  by  all  the  land-holders  of  the  irrigated 
plain  of  Valencia,  "  according  to  what  had  been  anciently 
established  and  practised  from  the  times  of  the  Saracens." 
Otherwise  irrigation  is  paid  for  either  by  the  year  or  for  a 
single  watering.  The  price  of  a  single  watering — reckoned  as 
consuming  180  to  200  cubic  metres  per  acre — varies  in  Alicante 
from  iod.  to  2 is.  an  acre ;  in  Lorca  the  price  is  los.  an  acre,  in 
Almansa  is.,  in  Granada  is.  Sd.  to  35.  $d.  When  irrigation  is 
paid  for  by  the  year,  the  annual  charges  are  as  follows :  in 
Catalonia,  on  an  average,  us.  2d.  an  acre;  on  the  canal  of 
Urgel  and  at  Malaga  igs.  *$d. ;  on  the  Esla  canal  £i ;  and  on 
the  Henares  canal  £1  gs.  The  wide  range  in  price  for  a 
single  watering  in  Alicante  is  due  to  variations  in  the  amount 
of  the  available  supply  and  in  the  dryness  of  the  season. 

In  countries  where  the  agricultural  classes  are  for  the  most 
part  little  educated,  it  is  best  for  all  interests  that  the  control 
of  the  irrigation  should  be  in  the  hands  of  the  Government. 
In  Egypt  and  in  the  British  possessions  in  India  irrigation  is 
so  administered.  The  responsibility  for  the  construction  of  the 
canal  works,  and  for  the  just  and  economical  distribution  of 
the  water,  rests  with  supervising  officers  of  the  higher  grades 
in  the  irrigation  service.  On  the  character  and  ability  of  these 
officers  depends  the  successful  and  satisfactory  working  of 
Government  irrigation  systems.  In  India  and  Egypt  this 
condition  of  success  has  not  been  wanting  ever  since  British 
engineers  have  been  the  responsible  officers. 

The  duties  of  the  Government  irrigation  engineers  are 
manifold.  « They  elaborate  the  project  for  the  irrigation  of  a 
tract  of  country,  and  design  the  works  of  supply,  distribution 
and  drainage  ;  they  arrange  for  and  superintend  the  con- 
struction of  the  works  ;  and,  lastly,  they  control  the  water 
distribution  of  the  completed  canal  system,  and  the  assess- 
ment of  the  water  revenue  derived  from  its  working.  As  part 
of  the  irrigation  system  the  flood  banks  of  the  river  are  in  their 


METHODS  OF   DISTRIBUTION    OF   WATER.  229 

charge,  to  be  maintained  as  a  defence  against  inundation  of 
cultivated  land.  Associated  with  the  maintenance  of  flood 
banks,  training  works  for  the  control  or  improvement  of  a  river 
have  often  to  be  undertaken.  Inland  navigation,  whether  on 
natural  waterways  or  on  artificial  channels,  falls  under  the 
care  of  the  irrigation  officer,  at  any  rate  in  India  and  Egypt. 
Land  reclamation  by  drainage  works  and  by  pumping  may  also 
be  added  to  the  list  of  his  duties.  In  India  he  may  even  be 
called  upon  to  do  magistrates'  work,  and  try  cases  and  sentence 
offenders  under  the  Irrigation  Act. 

The  Irrigation  Branch  of  the  Public  Works  Department  in 
India  is  thus  constituted :  A  chief  engineer  is  at  the  head  of 
the  establishment  of  the  province  ;  under  him  are  superintend- 
ing engineers  of  "  circles,"  who  have  jurisdiction  over  areas 
including  500,000  to  1,000,000  acres  of  irrigation :  next  come 
the  executive  engineers,  who  control  "  divisions,"  comprising 
sometimes  200,000  acres  of  irrigation.  The  executive  engineer 
is  the  officer  who  is  responsible  for  the  proper  assessment  of 
the  irrigation  revenue ;  it  is  his  duty  also  to  arrange  for  the 
repairs  of  the  works,  to  prepare  projects  for  the  improvement 
of  his  division,  and  to  secure  the  proper  regulation  and 
distribution  of  the  canal  water.  He  is  assisted  by  a  large 
establishment  of  Government  officials,  chiefly  composed  of 
natives  of  India,  who  live  in  the  various  "  sub-divisions  "  and 
"  sections  "  into  which  the  division  is  divided. 

In  Egypt  the  Irrigation  Department  is  a  branch  of  the 
Public  Works  Ministry,  which  is  under  a  minister,  assisted  by 
an  under-secretary  of  state.  The  irrigation  service  is  under 
two  inspectors-general,  one  for  Upper  Egypt,  and  the  other  for 
Lower  Egypt.  Under  the  inspectors-general  are  inspectors 
of  irrigation,  and  under  them  again  directors  of  works  and  chief 
and  district  engineers.  Each  inspector-general's  charge  com- 
prises from  3,000,000  to  3,500,000  acres  of  irrigated  land.  The 
inspectors  of  irrigation  have  charge  of  "  circles,"  comprising 
areas  of  500,000  to  1,000,000  acres.  The  controlling  staff 


23O  IRRIGATION. 

includes  also  an  inspector-general  for  headquarters  and  another 
for  basin  conversion  works.  The  duties  of  an  inspector  of  irriga- 
tion in  charge  of  a  circle  are,  if  not  the  most  important,  at  any 
rate  the  heaviest  of  all. 

Java  is  in  a  transition  stage  as  regards  methods  of  adminis- 
tration in  irrigation  matters.  Experimental  establishments, 
regulations  and  methods  of  distribution  do  not  seem  as  yet  to 
have  led  to  any  definite  conclusions  as  to  what  is  the  best  to 
adopt.  The  general  idea  on  which  the  experiments  are  based 
is  to  divide  the  island  into  fourteen  irrigation  circles,  each  of 
which  would  contain  the  entire  catchment  basin  of  one  or  more 
rivers,  irrespective  of  the  political  frontiers  of  the  provinces. 
Each  circle  would  be  put  in  the  charge  of  an  engineer  with  a 
proper  staff.  The  circle  engineers  would  be  under  the  chief 
engineer,  who  is  the  head  of  the  public  works  division,  and 
they  would  be  the  technical  advisers  of  the  residents  and 
their  provincial  officers.  The  experimental  organisation  of 
the  Javan  irrigation  service  has  points  of  resemblance  to  the 
administrative  arrangements  of  both  India  and  Egypt. 

Though  it  may  be  best  for  countries  with  native  agriculturists, 
such  as  those  of  India  and  Egypt,  to  have  their  irrigation 
administered  by  Government,  it  does  not  follow  that  there  is 
not  a  better  way  for  countries  with  an  agricultural  class  more 
advanced  in  civilisation.  A  good  example  of  self-government 
in  irrigation  matters  is  given  by  Sir  C.  Scott-Moncrieff  in  his 
British  Association  Address,  already  quoted  from  more  than 
once.  He  describes  how  these  things  are  managed  in  Pied- 
mont, in  Italy:  "The  Irrigation  Association  west  of  the  Sesia 
takes  over  from  the  Government  the  control  of  all  the  irrigation 
lying  between  the  left  bank  of  the  Po  and  the  right  bank  of  the 
Sesia.  The  Association  purchases  from  the  Government  from 
1,250  to  1,300  cubic  feet  per  second.  In  addition  to  this  it  has 
the  control  of  all  the  water  belonging  to  private  canals  and 
private  rights,  which  it  purchases  at  a  fixed  rate.  Altogether 
it  distributes  about  2,275  cubic  feet  per  second,  and  irrigates 


METHODS  OF   DISTRIBUTION   OF   WATER.  231 

therewith  about  141,000  acres,  of  which  rice  is  the  most 
important  crop.  The  Association  has  14,000  members  and 
controls  9,600  miles  of  distributary  channels.  In  each  parish 
is  a  council,  or,  as  it  is  called,  a  consorzio,  composed  of  all  land- 
owners who  take  water.  Each  consorzio  elects  one  or  two 
deputies,  who  form  a  sort  of  water  parliament.  The  deputies 
are  elected  for  three  years,  and  receive  no  salary  *  The 
assembly  of  deputies  elects  three  committees — the  direction- 
general,  the  committee  of  surveillance,  and  the  council  of 
arbitration.  The  first  of  these  committees  has  to  direct  the 
whole  distribution  of  the  waters,  to  see  to  the  conduct  of  the 
employes,  etc.  The  committee  of  surveillance  has  to  see  that 
the  direction-general  does  its  duty.  The  council  of  arbitration, 
which  consists  of  three  members,  has  most  important  duties. 
To  it  may  be  referred  every  question  connected  with  water 
rates,  all  disputes  between  members  of  the  Association,  or 
between  the  Association  and  its  servants,  all  cases  of  breaches 
of  rule  or  of  discipline.  It  may  punish  by  fines  any  member  of 
the  Association  found  at  fault,  and  the  sentences  it  imposes 
are  recognised  as  obligatory,  and  the  offender's  property  may 
be  sold  up  to  carry  them  into  effect.  An  appeal  may  be  made 
within  fifteen  days  from  the  decisions  of  this  council  of  arbitra- 
tion to  the  ordinary  law  courts,  but  so  popular  is  the  council 
that,  as  a  matter  of  fact,  such  appeals  are  never  made." 

In  Spain  there  exists  a  parallel  to  the  Piedmont  method  of 
administration.  The  irrigation  syndicate  of  Valencia  was  the 
first  "tribunal  of  waters"  to  be  created  specially  for  the  trial 
of  irrigation  cases.  It  sits  in  the  open  air,  upon  the  porch  of 
the  side  door  of  the  Cathedral,  and  settles  all  questions  relating 
to  irrigation  that  are  brought  before  it.  There  is  no  appeal 
against  its  decisions.  The  institution,  which  is  of  Moorish 
origin,  is  very  popular  in  Spain,  and  has  been  imitated,  with 
more  or  less  success,  by  all  the  other  syndicates  of  the 
country. 

The    regulations     concerning     the     granting    of    irrigation 


232  IRRIGATION. 

concessions  in  Spain  contain  a  condition  which  is  worthy  of 
special  note.  The  prospective  irrigators  are  bound  to  form  a 
syndicate  among  themselves,  even  when  the  water  supply  is 
conceded  to  a  company  which  is  authorised  to  recoup  itself  for 
its  outlay  by  levying  an  annual  payment  for  a  fixed  number  of 
years.  The  syndicate,  on  the  one  hand,  is  better  able  as  a  body 
to  protect  its  own  interests  in  its  dealings  with  the  company 
than  individuals  would  be  ;  and,  on  the  other  hand,  the  com- 
pany's relations  with  the  irrigating  community  are  facilitated 
by  their  having  a  duly  recognised  body  of  representatives  to 
deal  with. 

The  system  of  canal  management  in  France  is  in  some 
repects  similar  to  that  of  Spain.  None  of  the  canals  of 
Southern  France  belong  to  Government.  With  the  exception 
of  the  case  of  the  Marseilles  Canal,  the  usual  agency  by  which 
canals  are  constructed  and  administered  is  an  association  of 
cultivators.  The  desire  of  the  French  Government  is  that 
those  who  use  the  water  should  organise  themselves  into 
associations,  or  syndicates,  with  authority  to  construct  and 
work  irrigation  canals  at  their  own  risk.  The  Government  aids 
the  undertaking  by  contributing  about  one  third  of  the  estimated 
cost  of  the  work,  and  supervises  the  work  as  far  as  it  considers 
necessary. 

In  America  no  well-devised  scheme  of  canal  administration 
has  as  yet  been  evolved,  but  there  is  a  tendency  to  admit  the 
necessity  for  public  control  of  irrigation.  The  pioneer  settlers, 
when  they  first  made  use  of  the  water  of  a  running  stream  for 
irrigating  their  land,  were  not  under  the  restraint  of  any  regula- 
tions as  to  the  time  of  opening  and  shutting  the  head-sluices, 
but  pleased  themselves  about  it.  When  the  needs  of  others 
compelled  the  introduction  of  some  management  of  the  water 
supply  and  the  drawing  up  of  regulations  as  to  its  use,  the 
farmers,  who  inherited  from  their  pioneer  predecessors  their 
habits  of  freedom  to  do  as  they  liked,  were  slow  to  submit  to  the 
imposed  restiaint.  When  application  to  the  law  courts  failed 


METHODS  OF   DISTRIBUTION    OF  WATER.  233 

in  its  effect,  the  irrigator,  who  was  deprived  of  his  supply  of 
water  through  illegal  use  of  it  by  someone  higher  up  the  stream, 
had  no  other  course  left  open  to  him  but  to  shut  down  the 
offender's  head-sluice  by  force.  Mr.  Elwood  Mead  in  his  paper 
read  at  the  International  Engineering  Congress,  1904,  gives  an 
example  of  such  a  case.  A  canal  owner  in  California  was 
asked  how  he  managed  to  protect  his  rights  in  the 
seasons  of  shortage ;  he  replied  that,  in  the  first  place,  he  had 
obtained  a  decision  establishing  his  legal  title  to  water ;  but 
that,  in  addition,  every  year  he  shipped  in  two  men  from 
Arizona  who  were  handy  with  a  gun,  and  that  between  the 
courts  and  the  guns  he  managed  to  get  his  share.  To  which 
Mr.  Mead  adds  this  comment :  "  Peace  and  prosperity  for  the 
individual  and  the  community  alike  depend  upon  public  control 
of  the  streams  and  the  enforcement  of  laws  by  men  of 
experience  and  administrative  ability  of  a  high .  order.  The 
greatest  weakness  of  American  irrigation  has  come  from  the 
failure  to  recognise  this."  Six  States  have,  however,  intro- 
duced government  administration  of  canals,  but  the  systems 
differ  so  widely  from  one  another  that  a  general  description 
applicable  to  all  cannot  be  made.  Still,  the  policy  of  one  State 
may  serve  as  an  illustration.  According  to  the  Wyoming  code, 
the  water  of  canals,  streams,  springs,  lakes  and  ponds  is  State 
property.  The  State  Engineer  is  the  president  of  a  board  of 
five  men  managing  this  property.  The  State  gives  irrigators 
free  use  of  the  water,  permits  for  this  being  issued  by  the  State 
Water  Board.  It  is  a  misdemeanour  to  take  water  without  such 
a  permit.  To  secure  it  intending  users  of  water  must  file  a 
map  and  description  to  show  the  position  of  the  proposed 
channel  or  reservoir  and  the  land  to  be  irrigated.  Permits  are 
refused  for  any  project  which  would  cause  injury  to  an  existing 
right.  But  when  permits  are  granted,  after  the  water  has  been 
actually  applied  to  the  land,  the  State  issues  a  certificate  of 
appropriation  which  describes  the  land  in  question.  These 
certificates  are  recorded  in  the  same  manner  as  land  laws.  In 


234  IRRIGATION 

order  to  protect  the  rights  thus  bestowed,  the  State  has  to 
control  the  distribution  of  the  water  when  there  is  not  enough 
for  all.  For  this  purpose  the  State  is  divided  into  four  divisions, 
and  these  are  sub-divided  into  forty  districts.  Each  district 
has  a  water  commissioner,  a  State  official  acting  under  the  direc- 
tion of  the  State  engineer.  In  times  of  deficient  supply  he 
raises  and  lowers  the  gates  in  such  a  manner  as  to  give  each 
channel  its  proper  share.  Head-gates  adjusted  by  the  com- 
missioner may  not  be  moved  by  the  owner.  The  commissioner 
has  authority  to  arrest  offenders,  or  he  can  call  on  the  sheriff  to 
do  so.  As  Mr.  Mead  remarks,  it  is  always  difficult  to  induce 
irrigators  to  submit  to  this  public  control,  but,  once  adopted,  it 
is  always  maintained.  It  relieves  irrigators  from  watching  their 
neighbours.  They  do  not  have  to  patrol  the  stream  at  night  to 
prevent  gates  being  raised  when  they  should  be  closed.  Where 
irrigators  have  to  defend  their  own  rights,  neighbours  are  always 
at  war.  Where  there  is  public  control  they  live  in  friendly  rela- 
tions with  each  other,  while  the  water  commissioner  is  often 
abused.  If  he  does  his  work  with  tact  and  justice,  he  becomes 
the  most  important  member  of  the  community,  and  contributes 
to  its  respect  for  law  and  order,  and  to  the  peace  of  mind  and 
well-being  of  the  irrigators  to  a  degree  which  has  to  be 
experienced  to  be  understood. 

Those  who  have  had  experience  of  irrigation  in  Egypt  during 
the  British  Occupation  will  understand  these  remarks  well. 
Before  a  real  control  was  exercised  over  the  distribution 
of  water  by  engineers  of  experience  and  honesty,  the  native 
irrigators,  during  the  period  of  water  scarcity,  used  to  settle 
among  themselves  all  irrigation  questions  by  breaking  each 
other's  heads  with  nabouts,  a  stout  stick  of  a  kind  convenient 
for  the  purpose.  When  the  inspector  of  irrigation  (corre- 
sponding to  the  water  commissioner  of  America)  assumed 
effective  control  of  the  working  of  the  canals,  the  summer  death- 
rate  due  to  water  disputes  declined,  and,  before  long,  perfect 
confidence  in  the  inspector's  justice  and  ability  was  established 


METHODS  OF   DISTRIBUTION    OF   WATER.  235 

It  is  seldom  now  that  any  agriculturist  in  Egypt  in  want  of 
water  takes  the  law  into  his  own  hands. 

But  before  all  else,  as  a  preliminary  to  any  scheme  of  canal 
administration,  the  right  of  the  public  to  the  natural  water 
supply  of  the  country  must  be  safeguarded  against  any  exclusive 
appropriation  by  individuals.  This  important  duty  should  not 
be  neglected  or  postponed  by  the  Government  of  any  country 
that  is  endowed  with  the  means  of  development  that  irrigation 
brings.  Rivers,  torrents,  streams,  and  all  natural  water- 
courses, and  the  water  that  flows  in  them,  should  be  declared 
by  decree  to  belong  to  the  public  domain.  In  Italy  and  Spain 
the  example  has  been  set  for  other  countries.  In  India  and 
Egypt  no  one  would  think  of  contesting  the  Government's 
right  to  possess  the  country's  natural  waterways.  According 
to  the  Wyoming  code  in  the  United  States,  which  served  above 
as  an  example  of  State  administration,  the  water  of  canals, 
streams,  springs,  lakes  and  ponds  is  made  State  property- 
France  has  stopped  short  of  a  thorough-going  State  policy  in 
respect  to  the  ownership  of  its  watercourses :  for,  though  irri- 
gation is  indispensable  in  the  south  of  France,  it  is  not  so  in 
Northern  and  Central  France.  The  country  as  a  whole  is 
more  interested  in  navigation  than  in  irrigation.  Consequently 
the  waterways  that  are  navigable  by  boats  or  rafts,  whether 
natural  or  artificial,  are  declared  to  be  the  property  of  the 
State.  Other  watercourses  belong  to  no  one,  but  the  riparian 
owners  of  land  have  the  right  of  using  the  water.  Nevertheless 
the  Government  exercises  a  supervision  over  all  these  water- 
ways, and  no  water  can  be  taken  for  purposes  of  irrigation 
without  a  special  permit  signed  by  the  prefect  of  the 
department. 

Sir  William  Willcocks,  in  his  Report  on  "  Irrigation  in 
South  Africa,  1901,"  lays  stress  on  the  necessity  of  establishing 
by  decree  that  all  rivers  and  natural  watercourses  are  part  of 
the  public  domain.  The  longer  this  action  is  postponed  the 
greater  will  be  the  difficulty  of  taking  it,  as  vested  interests  to 


236  IRRIGATION. 

be  overcome  will  grow  in  number  and  strength  with  the 
development  of  the  country.  More  especially  is  it  necessary 
to  take  this  step  in  South  Africa,  as  the  only  possible  means  of 
promoting  the  agricultural  development  of  the  country  seems 
to  be  by  means  of  water  storage ;  and,  if  water  storage  is  the 
solution  of  the  agricultural  problem,  Government  must  under- 
take the  work.  The  construction  of  dams  and  the  formation 
of  reservoirs  with  their  distributing  canals  are  undertakings  too 
vast  for  private  enterprise,  and  they  affect  the  prosperity  of  so 
wide  an  area  that  the  State  should  assume  the  responsibility 
for  their  construction  and  subsequent  management. 


CHAPTER  XL 

FLOOD   BANKS  AND    RIVER  TRAINING. 

IF  perennial  irrigation  is  given  to  lands  which  have  hitherto 
been  subject  to  inundation  from  the  flood  of  a  river,  the  crops 
that  will  thereafter  be  standing  on  the  ground  during  the  flood 
season  must  be  secured  against  submersion  by  the  construction 
of  protective  banks.  As  the  deltas  of  rivers  are  formed  by  the 
deposit  of  recurring  floods,  the  highest  land  so  formed  cannot 
be  above  the  reach  of  a  maximum  flood.  Consequently,  when 
a  river  delta  is  brought  under  perennial  irrigation,  it  is  neces- 
sary to  protect  it  by  making  river  banks  to  prevent  the  floods 
from  spilling  sideways  and  flowing  across  country.  But  the 
confinement  of  the  flood  discharge  to  the  main  channel  or 
channels  of  the  river  is  interfering  with  the  natural  process 
by  which  the  land  level  has  been  hitherto  gradually  raised, 
so  that  henceforward  the  raising  of  the  land  surface  will, 
if  it  does  not  altogether  stop,  proceed  at  a  much  slower 
rate  than  in  the  past.  At  the  same  time  the  amount  of  silt 
carried  by  the  river  and  deposited  at  its  mouth,  where  it 
meets  the  sea,  will  be  at  least  as  much  as  before,  and  the 
rate  at  which  the  river  bed  will  rise  in  consequence  of  the 
yearly  increasing  deposit  will  remain  undiminished.  The 
river  bed  will,  therefore,  rise  at  a  more  rapid  rate  than 
the  land  surface  alongside  it,  and  with  it  also  the  heights 
of  floods.  Consequently  it  will  be  found  necessary  from 
time  to  time  to  add  to  the  height  of  the  flood  protective 
embankments,  which  may  thus,  after  a  sufficient  period,  become 
inconveniently  high.  It  has  been  calculated  from  the  evidence 


238  IRRIGATION. 

of  ancient  monuments  that  the  lower  portions  of  the  Nile 
Valley  and  its  delta  have  been  raised  by  the  natural  action  of 
the  river  at  the  rate  of  4  inches  a  century.  If,  in  consequence 
of  the  construction  of  Nile  banks  on  perennial  irrigation  being 
introduced  in  the  delta,  the  further  raising  of  the  land  surface 
has  been  stopped  while  that  of  the  river  bed  continues,  it  will 
be  found  a  thousand  years  hence  that  the  crest  of  the  banks, 
if  maintained  at  the  same  height  above  highest  flood  as  is  the 
rule  to-day,  will  have  to  be  3  feet  4  inches,  or  a  metre  higher 
than  they  are  now  above  mean  sea  level. 

There  is  another  respect  in  which  natural  arrangements  are 
upset  by  the  construction  of  river  protective  banks.  When 
artificial  control  is  absent,  the  flood  in  the  river  branches  of  a 
delta  finds  its  way  to  the  sea  not  only  along  the  main  channels, 
but  also  by  spill  channels  along  which  part  of  the  river  dis- 
charge flows  at  high  flood.  Below  the  take-off  of  each 
successive  spill  channel  there  is  a  decrease  in  the  discharge 
which  the  main  channel  has  to  carry.  Consequently  the  dis- 
charging capacity  of  the  river  channel,  which  adapts  itself  to 
the  work  it  has  to  do,  constantly  diminishes  from  the  head  to 
the  tail.  Now,  when  these  spill  channels  and  all  side  escapes 
for  the  flood  water  are  closed  by  river  protective  banks,  the 
whole  flood  discharge  will  flow  forwards  along  the  proper 
channel  of  the  river;  and,  since  the  dimensions  of  the  channel 
diminish  towards  the  tail,  the  flood  levels  in  the  lower  reaches 
will  rise  higher,  relatively  to  the  land  alongside  the  river,  than 
they  did  before  the  spill  channels  were  closed,  necessitating  the 
raising  of  the  flood  embankments  to  contain  the  floods.  This 
consideration  will  affect  the  question  as  to  how  far  down  the 
river  branches  it  is  advantageous  to  extend  the  river  banks  and 
to  prevent  the  river  spilling  sideways. 

In  the  delta  of  Egypt  the  level  of  a  high  flood  in  one  of  the 
branches  is  from  3*0  to  3*5  metres  (about  10  to  uj  feet)  above 
country  level.  These  levels  are  attained  in  the  middle  third  of 
the  Damietta  branch.  At  the  head  of  the  branch  the  height  of 


FLOOD   BANKS   AND   RIVER   TRAINING. 


239 


an  extreme  flood  above  country  level  does  not  exceed  2  metres 
(6J  feet).  At  Damietta,  15  kilometres  above  the  meeting  with 
the  sea,  the  flood  falls  to  country  level.  The  dimensions, 
adopted  of  late  years,  for  the  Nile  banks  of  Lower  Egypt  are 
shown  in  Fig.  65. 

Fig.  65  A  gives  the  section  when  the  high  flood  level  is  not 

NILE    BANKS 

Dimensions    •  »   Metre* 

FIG 


H.F.L.. 


more  than  half  a  metre  above  the  country  level  inside  the 
banks.  If  the  soil  is  sandy,  the  crest  width  is  increased  to  4 
metres.  The  same  crest  width  of  4  metres  is  also  given  to  the 
bank  if  it  is  used  as  a  road. 

Fig.  65  B  gives  the  section  when  the  high  flood  level  is  over 
half  a  metre  but  not  more  than  i  metre  above  the  country 
level.  If  the  bank  is  used  as  a  road,  the  crest  width  is 
increased  to  5  metres. 


240  IRRIGATION. 

Fig.  65  C  gives  the  section  when  the  high  flood  level  is  over 
i  metre  but  not  more  than  2  metres  above  country  level; 
and  Fig.  65  D  when  it  is  over  2  metres  above  country  level. 

If  infiltration  takes  place  to  any  considerable  extent  the 
lower  slopes  of  the  bank  on  the  land  side  are  made  three  to  one, 
or  even  flatter,  as  experience  may  show  to  be  necessary.  If  the 
soil  is  very  sandy,  it  is  better  to  make  the  slopes  three  to  one 
and  to  omit  the  land  side  berms. 

In  India,  America  and,  in  fact,  most  countries,  the  slopes  of 
the  banks  are  always  turfed ;  but  in  Egypt  they  are  left  bare, 
for  the  very  good  reason  that  there  is  no  grass  for  turfing  to  be 
found,  and  there  is  no  rain  to  keep  grass  alive  if  grown  from 
seed. 

In  America  flood  embankments  are  termed  "  levees."  The 
usual  dimensions  for  a  levee  in  the  United  States  are  8  to  10 
feet  of  crest  width  and  slopes  of  3  to  i.  If  the  soil  is  sandy  the 
top  width  is  sometimes  made  15  feet  and  the  slopes  5  to  i.  If 
the  bank  is  high,  a  berm  about  20  feet  in  width  is  added  on  the 
land  side,  some  8  feet  below  the  top  of  the  levee,  and  the  slope 
of  the  bank  below  the  berm  is  made  flatter  than  the  slope 
above. 

In  Italy,  the  Po  embankments  have  a  crest  width  of  from  23 
to  26  feet,  sometimes  reduced  to  16  feet.  The  side  slopes  are 
formed  at  2  to  i  or  3  to  i.  There  are  usually  two  berms  on  the 
land  side. 

On  the  Rhine,  the  river  banks  have  a  top  width  of  only  6  or 
7  feet,  which  is  doubled  when  the  crest  is  utilised  as  a  road. 
The  slopes  are  made  3  to  I. 

In  constructing  flood  embankments  the  precautions  taken  to 
ensure  safety  vary  considerably  in  different  countries.  It  is 
remarkable  what  a  simple  matter  the  construction  of  a  bank  is 
in  Egypt,  and  what  few  precautions  are  taken.  The  banks  are 
thrown  up  without  any  special  preparation  of  the  land  surface 
on  which  they  are  to  be  made ;  the  soil  is  not  deposited  in 
layers,  nor  watered,  nor  rammed.  The  large  clods  are  broken 


FLOOD  BANKS  AND   RIVER  TRAINING.  24! 

up,  and  the  excavation  pits  are  kept  at  a  certain  distance  from 
the  outside  toes  of  the  finished  bank.  But  this  is  all.  And  yet 
there  is  no  rain'  to  consolidate  the  new  earthwork,  nor  is  there 
turf  to  protect  the  slopes.  The  banks  do  not  breach,  at  any 
rate  from  the  pressure  of  water.  If  they  did  breach  for  want  of 
more  elaborate  methods  of  construction,  more  precautionary 
measures  to  obtain  security  would  by  now  have  been  introduced. 
Probably  the  dimensions  given  to  the  banks  in  Egypt  are 
sufficiently  liberal  to  dispense  with  the  methods  of  construction 
which  are  imperative  with  banks  of  comparatively  slight 
section. 

When  a  breach  occurs  it  is  almost  always,  if  not  always, 
found  to  be  due  to  causes  other  than  that  of  direct  water- 
pressure.  Some  soils  become  waterlogged  and  lose  their  power 
of  supporting  weight.  When  this  happens  below  a  high  bank 
subject  to  a  considerable  head,  the  soil  supporting  it  may  give 
way  and  cause  a  subsidence  of  the  bank,  sufficient  sometimes 
to  allow  the  water  that  is  being  retained  to  flow  over  the  top 
of  the  bank  and  breach  it.  In  such  cases  it  is  better  to  spread 
the  weight  over  a  broad  base  by  giving  the  bank  flat  slopes  or 
frequent  berms,  and  also  to  keep  the  borrow  pits  at  a  safe 
distance,  so  that  the  natural  soil  may  remain  intact  to  resist 
settlement. 

Sometimes  wave  action  may  cause  a  breach,  if  a  bank  is  left 
at  its  mercy  without  protection.  But  this  seldom  happens ; 
and  when  it  does  it  is  due  to  negligence  on  the  part  of  the 
watchmen  whose  duty  it  is  to  guard  the  bank.  For  the  erosion 
effected  by  waves  is  more  or  less  gradual,  and  the  attack  being 
made  at  water  surface  can  be  combated  and  successfully  resisted 
if  adequate  means  have  been  provided  to  meet  such  a  danger. 
Light  poles,  or  bamboos,  and  bundles  of  long  grass  or  maize 
stalks,  or  any  such  material  that  happens  to  be  obtainable  in 
the  neighbourhood,  should  be  collected  on  the  banks  before  the 
flood  season,  ready  for  use  as  required. 

A  fruitful  source  of  danger  is  the  existence  of  ill-constructed 

I.  R 


242  IRRIGATION. 

culverts  made  in  the  banks  to  irrigate  land  immediately  inside 
them.  Such  works  should  never  be  allowed  unless  they  ate 
built  to  an  approved  design  and  under  the  supervision  of 
Government  officers  or  responsible  representatives  of  the 
public  who  are  interested  in  the  safety  of  the  banks. 

There  is  one  other  and  more  formidable  danger  to  which 
river  banks  are  subject.  The  most  frequent  cause  of  breaches 
is  the  undermining  action  of  the  flowing  river  along  reaches 
where  the  soil  of  its  margins  is  light  and  the  velocity  of  its 
current  high.  If  precautions  to  meet  this  danger  are  post- 
poned till  the  flood  has  come,  the  chances  of  successfully 
meeting  it  are  slight,  except  at  ruinous  expenditure.  If  the 
river  embankment  is  close  to  the  river  edge  and  the  river  in 
flood  begins  to  undermine  it,  it  is  often  lost  labour  and 
material  to  throw  stone  into  the  deep  water,  or  drive  in  stakes 
along  the  river  front,  while  the  cutting  action  goes  on  below 
the  foot  of  the  stakes.  If  there  is  danger  of  a  breach,  the  only 
safe  thing  to  do  is  to  quickly  throw  up  a  retired  bank  at  some 
distance  behind  the  threatened  length,  so  that  it  may  take  up 
the  duty  of  protecting  the  country  from  inundation  in  the 
event  of  the  original  bank  being  breached.  While  the  safety 
bank  is  being  made,  the  river  attack  on  the  original  bank  must 
be  held  in  check  and  its  advance  delayed  by  the  best  means 
available  under  the  particular  circumstances  of  the  case. 

It  is,  however,  much  safer  and  more  economical  to  anticipate 
and  guard  against  the  danger  of  undermining  during  the  low 
supply  season  that  precedes  the  flood.  There  are  two  ways  of 
doing  this.  The  bank  may  be  retired  along  the  threatened 
lengths  to  a  safe  distance  from  the  river  edge  beyond  the 
reach  of  danger ;  or  the  points  and  lengths  liable  to  suffer 
erosion  may  be  protected  by  spurs  and  revetments  of  sufficient 
power  of  resistance  to  be  relied  upon.  The  latter  method  is 
adopted  in  the  front  of  villages  and  wherever  a  retirement  is 
impossible  or  objectionable.  Otherwise  the  former  method  by 
retreat  is  generally  preferable.  But  better  than  either  method 


FLOOD   BANKS  AND   RIVER   TRAINING.  243 

is  a  combination  of  the  two.  The  retirement  of  the  bank  from 
the  river  edge  to  a  distance  of  about  50  yards,  and  the  preven- 
tion of  further  encroachment  by  the  construction  of  spurs,  is 
the  most  satisfactory  arrangement.  The  river  bank  would 
then  be  safe  from  any  risk  of  being  undermined,  and  its  retire- 
ment would  not  have  to  be  repeated  in  the  future  in  consequence 
of  further  advances  of  the  river.  Spurs  as  a  form  of  defence 
against  encroachment  are  preferable  to  revetments  of  the 
slope,  as  they  are  more  efficient  and  economical,  and,  when 
once  established,  require  less  attention  than  revetments.  But 
as  the  eddy  created  down  stream  of  a  spur  eats  into  the  bank 
for  a  certain  distance,  this  method  cannot  be  adopted  where 
the  bank  to  be  protected  is  not  sufficiently  retired  from  the 
river  edge  to  be  outside  the  limits  of  the  eddy's  action.  In 
such  a  case  the  river-side  slope  must  be  protected  by  a  revet- 
ment of  stone  or  other  suitable  material  which  will  offer 
sufficient  resistance  to  prevent  encroachment  at  any  point. 

The  material  used  in  the  construction  of  river  spurs  and 
revetments  may  be  stone,  brick,  brushwood,  or  any  other 
suitable  material  that  may  be  readily  procurable.  Stone  or 
brick  has  the  advantage  of  durability,  and  may  therefore  in  the 
long  run  prove  to  be  a  more  economical  material  to  use  than 
brushwood. 

The  forms  given  to  spurs  are  various.  The  diversity  is  due, 
probably,  to  the  different  conditions  existing  at  the  places 
where  spurs  are  found  necessary.  In  India,  a  form  much 
favoured  is  the  T  form,  which  has  at  its  outer  end  a  certain 
length  of  spur  face  parallel  to  the  desired  direction  of  flow 
designed  to  guide  the  current.  This  would  be  an  expensive 
arrangement  if  the  spur  were  to  extend  into  deep  water. 

In  Plate -V.  is  shown  a  form  of  spur  existing  in  Spain.  A 
timber  gridiron,  resting  against  a  weighted  tripod,  forms  a 
support  for  the  smaller  material,  such  as  brushwood,  by  which 
the  obstruction  to  the  current  is  formed. 

The  usual  f jrm  of  spur  adopted  in  Egypt  has  its  axis  inclined 

R  2 


244  IRRIGATION. 

at  120  degrees  to  the  direction  of  the  current.  It  has  a  sloping 
crest,  commencing  at  the  shore  end  from  a  point  about  2  feet 
above  highest  flood  level,  and  carried  down  to  a  point  about 
3  feet  above  low  water  level  at  the  outer  end.  The  slope  of 
the  crest,  therefore,  depends  upon  the  length  that  it  may  be 
decided  to  give  to  the  spur.  Usually  it  is  about  5  to  i.  The 
crest  width  is  made  from  3  to  6  feet,  and  the  side  and  end 
slopes  are  formed  at  I  to  i.  The  spur  is  connected  by  an 
earthen  "  tie-back  "  with  the  river  bank  behind  it,  so  that  the 
flood  may  not  take  it  in  rear.  The  river  side  slopes  imme- 
diately above  and  below  the  spur  are  revetted  for  short  distances 
to  protect  the  root  of  the  spur  from  the  action  of  eddies. 

Similar  spurs  are  also  sometimes  made  for  the  protection  of 
the  sides  of  large  canals  which  at  full  supply  have  a  discharge 
of  such  volume  and  velocity  that  the  side  slopes  suffer  from 
erosion.  Spurs  intended  for  such  a  purpose  are  made  in  pairs, 
one  spur  on  either  side  of  the  canal,  and  they  are  formed  with 
their  axes  at  right  angles  to  the  current.  In  other  respects 
thev  resemble  river  spurs,  but  the  position  of  the  outer  ends, 
and  the  slope  to  be  given  to  the  crest,  are  determined  by 
considerations  other  than  those  that  apply  to  river  spurs. 
When  the  conditions  of  soil  and  discharge  are  such  that  the 
sides  of  a  canal  succumb  to  erosive  action,  the  eroded  material 
is  carried  forward  by  the  water  and  spread  about  over  the  bed 
of  the  canal  further  down.  Consequently  when,  as  the  season 
advances,  the  water  level  falls  with  a  decreasing  discharge,  the 
obstruction  to  the  flow,  caused  by  the  deposits  of  eroded 
material,  seriously  affects  the  available  water  supply.  It  is 
therefore  important  to  prevent  such  deposits  by  stopping 
erosion.  The  proper  distance  apart  of  the  opposing  spurs  01 
any  pair  depends  on  the  discharges  of  the  canal,  the  object 
being  to  produce  and  maintain  a  channel  of  uniform  section 
and  of  such  dimensions  that  it  will  carry  its  discharge  without 
any  scour  or  deposit  taking  place.  A  practical  way  of  deter- 
mining the  width  of  bed  to  be  allowed  between  the  toes  of 


FLOOD   BANKS   AND   RIVER   TRAINING.  24$ 

two  opposing  spurs  is  to  study  a  longitudinal  section  of  the 
bed  made  after  a  flood  season,  and  so  to  discover  the  points  at 
which  the  bed  has  remained  at  the  correct  level,  having  been 
neither  lowered  by  scour  nor  raised  by  deposit  below  or  above 
that  level,  Cross  sections  taken  at  these  points  will  give  the 
dimensions  of  the  channel,  adapted  to  the  conditions  of  the 
canal,  which  it  is  desired  to  determine.  The  spurs  should  be 
constructed  so  that  the  waterway  allowed  at  high  flood  levels 
between  the  opposing  spurs  of  a  pair  may  approximate  to  that 
of  the  selected  cross  sections  ;  or  be  a  little  less,  as  the  velocity 
of  current  must  always  be  accelerated  to  a  certain  extent 
between  the  spurs  if  they  perform  the  work  of  directing  the 
flow.  The  interval  between  one  pair  and  the  next  pair  of 
spurs  should  be  such  that  the  effect  of  one  pair  shall  begin 
where  that  of  the  next  pair  ends.  Usually  the  distance  would 
be  from  200  to  300  yards.  Experience  of  the  actual  working 
of  such  spurs  on  the  four  largest  canals  in  Egypt  has  demon- 
strated that  they  are  a  most  efficient  means  of  checking  erosion 
of  the  banks  and  of  diminishing  thereby  the  resulting  deposits 
along  the  canal  bed.  The  section  of  the  canal  is  gradually 
restored  by  them  to  its  correct  width  and  depth,  and  theberms, 
which  had  been  cut  away,  are  reformed  by  a  deposit  of  silt  on 
the  sides  of  the  channel  between  the  pairs  of  spurs. 

River  protective  works,  such  as  spurs  to  protect  dangerous 
points  against  erosion,  are  different  in  their  object  from  river 
training  works.  Canal  spurs  which  are  made  with  the  object 
of  stopping  erosion,  and  also  of  producing  a  regular  channel  of 
uniform  section,  partake  of  the  nature  of  both  protective  and 
training  works.  River  protective  works  have  usually  to  b 
made  in  the  deep  water  which  is  to  be  found  at  threatened 
points;  river  training  works  are  generally  carried  out  in 
shallow  water.  The  former,  by  strength  of  material,  forcibly 
prevent  the  river  from  injuring  its  banks;  the  latter,  by  gentle 
persuasion,  induce  it  to  flow  in  the  direction  and  behave  in  the 
manner  desired.1 

»  See  Note  9,  Appendix  IV. 


246  IRRIGATION. 

River  training  works  maybe  undertaken  for  different  objects. 
They  may  be  designed  in  the  interests  of  irrigation,  or  of  navi- 
gation, or  for  the  purpose  of  reclaiming  land  ;  sometimes  also 
for  the  sake  of  diverting  the  river  channel  from  a  too  dangerous 
proximity  to  an  important  town,  building  or  property  of 
sufficient  value  to  justify  the  expense  involved. 

It  is  often  necessary  to  train  the  river  for  some  distance 
up  stream  of  the  head  works  of  a  canal  system,  in  order  that 
the  discharge  may  flow  in  a  regular  channel  and  correct  direc- 
tion as  it  approaches  the  weir  or  other  river  work  of  regulation. 
In  India  the  river  Ganges  is  trained  above  and  below  the 
Narora  weir,  at  the  head  of  the  Lower  Ganges  canal,  for 
21  \  miles,  by  works  on  both  banks  above  the  weir  and  on  the 
right  bank  below  it.  The  training  works  consist  of  groynes 
constructed  in  pairs  at  half-mile  intervals,  each  groyne  being 
tied  back  to  the  high  ground,  canal  or  parallel  bank  behind  it, 
so  as  to  confine  the  river  discharge  to  the  passage  between  the 
heads  of  the  opposing  pairs  of  groynes,  and  prevent  any  flow 
of  flood  water  behind  the  groynes.  The  distance  between  the 
heads  of  the  groynes  is  3,000  feet,  which  is  the  normal  width 
of  the  river.  After  groynes  of  various  patterns  and  different 
materials  had  been  experimented  with,  the  type  eventually 
adopted  as  the  most  efficient  was  the  T-headed  form,  and  the 
material  employed  was  earth  with  rubble-stone  facing  and  toes. 
The  cross  head  of  the  T  groyne  was  made  400  feet  long,  with 
an  up-stream  length  of  300  feet  and  a  down-stream  length  of 
100  feet.  The  stalk  of  the  T,  or  axis  of  the  groyne,  was  placed 
at  right  angles,  and  the  cross  head  parallel,  to  the  direction  of 
flow.  Large  masses  of  kankar  (nodular  limestone)  were  stacked 
on  the  slopes  of  the  groynes  ready  to  subside  into  any  hole 
scoured  out  below  them.  The  works  have  been  successful  in 
training  the  river,  but,  like  most  training  works,  they  have  been 
costly  to  execute. 

The  type  of  spur  already  described  under  protective  works 
as  the  favoured  form  in  Egypt  is  made  entirely  of  loose  stone, 


FLOOD    BANKS   AND   RIVER   TRAINING,  247 

the  tie-back  only  being  of  earth.  Consequently,  if  a  settlement 
at  the  outer  end  takes  place,  it  does  not  necessarily  follow  that 
the  consequences  are  serious.  It  is  in  fact  expected  that  newly- 
made  spurs  will  settle  for  two  or  three  years  after  their  con- 
struction. If  they  do,  they  are  repaired  and  made  up  to  full 
section  as  often  as  the  necessity  arises,  until  at  last,  as  the 
result  of  repeated  settlements,  the  bottom  stone  reaches  such  a 
low  level  in  the  river  bed  that  the  scour  of  the  current  past  the 
end  of  the  spur  no  longer  disturbs  it,  and  stability  is  at  length 
reached.  A  spur  of  this  description  can  also  be  added  to  and 
lengthened  by  degrees  after  it  has  become  established  and 
stable,  so  that  the  effect  on  the  river  may  be  produced  by  a 
gradual  process.  Powers  of  persuasion  and  not  of  violence 
should  characterise  training  works  of  discretion.  Another 
virtue  that  the  spur  with  sloping  crest  possesses  is  that  the 
eddy  produced  down  stream  is  of  comparatively  little  violence, 
as  the  obstruction  is  presented  to  the  flow  in  a  gradually 
increasing  form  from  the  outer  toe  in  deep  water  to  the  root  of 
the  spur  where  it  rises  above  high  flood  level  and  unites  with 
the  tie-back. 

In  Egypt  training  works  have  been  undertaken  at  the  apex  of 
the  Delta  to  induce  the  river  to  bifurcate  at  the  selected  point, 
so  that  the  twin  channels  may  flow  symmetrically  on  to  the 
barrages  which  span  the  two  branches,  and  in  a  direction  at 
right  angles  to  the  face  of  either  work.  The  training  works 
consist  of  spurs  to  stop  any  encroachments  taking  place  in  a 
wrong  direction,  and  to  encourage  them  when  they  take  a  right 
direction ;  of  revetments  to  preserve  the  river  slopes  which 
coincide  with  the  sides  of  the  ideal  channels  to  be  formed  ;  and 
of  a  bar  of  anchored  mimosa  trees,  renewed  every  year,  across 
the  upper  end  of  a  side  branch  of  the  river  which  it  is  desired 
should  close  itself  by  a  deposit  of  silt. 

In  Egypt,  also,  training  works  have  been  undertaken  by  a 
company  with  the  object  of  reclaiming  land  in  the  bed  of  the 
river.  The  works,  for  the  most  part,  take  the  form  of  a 


248  IRRIGATION 

regulator  at  the  lower  end  of  a  reach,  the  bed  of  which  is  to  be 
reclaimed.  By  means  of  the  regulator  the  flow  is  checked 
during  the  flood  season,  so  as  to  produce  a  velocity  most 
favourable  to  the  deposition  of  silt.  The  bed  level  is  raised  by 
the  deposit  of  successive  floods  until  it  is  high  enough  to  be 
cultivated.  The  silting  up  of  side  channels,  for  the  object  of 
reclamation,  often  effects  an  improvement  in  the  navigable 
conditions  of  the  river. 

1  The  deposition  of  silt  behind  spurs  takes  place  more  readily 
if  the  spurs  are  permeable  than  if  they  are  impermeable.  Spurs 
made  of  loose  rubble  are  permeable  so  long  as  the  interstices 
between  the  stones  do  not  silt  up ;  and  this  will  only  occur 
at  the  same  rate  at  which  the  silt  deposit  forms  down 
stream  of  the  spur,  to  which  there  is  no  objection.  Permea- 
bility is  obtained  sometimes  by  making  the  spurs  of  bushy 
trees  or  brushwood  ;  and,  in  certain  situations,  such  material  is 
preferable  to  stone.  But  stone  is  the  more  durable,  and  if  the 
action  of  the  spur  is  to  be  continuous  and  to  extend  beyond  a 
period  of  a  few  years  only,  it  is  to  be  preferred  as  the  material 
of  construction ;  unless  practical  considerations,  such  as  the 
abundance  of  other  suitable  material  close  at  hand,  or  the 
prohibitive  cost  of  stone,  call  for  its  rejection.  The  existence 
of  abundance  of  cotton-wood  and  willows  on  the  Mississippi 
river  determined  the  choice  of  material  for  the  important 
training  works  undertaken  in  the  interests  of  the  navigation  of 
that  river.  The  aim  of  the  engineers  who  direct  the  training 
works  of  the  Mississippi  is  to  obtain  a  uniform  channel,  and  so 
to  prevent  alterations  in  the  velocity  of  the  current,  to  which  is 
attributed  the  mischief  of  undermining  banks  and  -consequent 
shoaling.  The  object  is  the  same  as  that  for  which  spurs,  as 
already  described,  have  been  made  in  the  large  canals  of  Egypt, 
but  the  means  employed  are  different.  The  cotton-wood  and 
willows,  woven  into  mattresses,  are  sunk  in  place  and  fixed 
along  the  sides  of  the  channel  to  be  regularised.  For  the 
protection  of  banks  "  mattress  revetment  is  the  chief  method 


FLOOD    BANKS  AND   RIVER   TRAINING.  249 

employed  along  the  Mississippi  and  Missouri  rivers.  The  brush 
grows  in  abundance,  and  in  spite  of  continued  denudation  for 
these  works  the  supply  has  not  been  exhausted,  as  cotton-wood 
and  willows  spring  up  rapidly,  so  that  it  is  the  cheapest 
material  for  use.  Out  of  the  abundance  and  cheapness  of  this 
material  has  grown  the  practice  of  its  use,  in  connection  with 
stone,  also  fairly  plentiful,  as  a  revetment  for  banks  in  this 
country  (U.  S.  America)."1 

1  "  The  Improvement  of  Rivers,"  by  B.  F.  Thomas  and  D.  A.  Watt. 


CHAPTER  XII. 

AGRICULTURAL    OPERATIONS   AND   RECLAMATION   WORKS. 

IT  has  already  been  shown  in  Chapter  III.  that  an  irrigation 
engineer  must  acquire  a  correct  knowledge  of  certain  agricul- 
tural matters  before  he  can  estimate  with  any  confidence  the 
quantity  of  water  that  the  canals  will  have  to  carry  at  different 
seasons.  In  fact  the  more  complete  his  knowledge  of  such 
matters,  the  more  competent  will  he  be  to  design  a  project 
adapted  to  the  needs  of  the  land  to  be  irrigated.  The  configura- 
tion of  the  ground,  the  nature  of  the  soil,  the  description  of  the 
crops,  the  seasons  of  sowing  and  harvest,  the  times  when  water 
is  needed,  the  habits  of  the  cultivators,  must  all  be  considered 
when  the  "  duty  "  of  water  for  the  prospective  canal  system  is 
being  determined.  Again,  when  the  financial  results  of  any  irriga- 
tion scheme  are  being  calculated,  it  is  not  enough  to  include  on 
the  expenditure  side  the  cost  only  of  the  canal  and  drainage 
works ;  but  an  allowance  must  be  made  for  the  sometimes 
considerable  expense  that  the  landowner  will  incur  in  preparing 
the  ground  for  the  application  of  irrigation.  The  ground  may 
have  to  be  levelled,  or  to  be  cleared  of  scrub  or  other  growth  ; 
but,  in  any  case,  field  channels,  or  ridges  to  divide  the  area  into 
compartments  or  terraces  for  flooding,  or  other  means  for  the 
internal  distribution  of  the  water,  must  be  provided.  The  cost 
of  these  private  operations  will  naturally  vary  with  the  condi- 
tions. M.  Salvador,  in  his  St.  Louis  paper  on  "  Irrigation  in 
France,"  states  that  it  may  be  estimated  at  from  500  to  800 
francs  per  hectare  (£8  to  £13  per  acre).  This  estimate  will 
appear  exaggerated  to  those  whose  experience  has  been  gained 
in  countries  where  the  agricultural  conditions  are  peculiarly 


AGRICULTURAL  OPERATIONS  AND  RECLAMATION  WORKS.      2$ I 

favourable  to  irrigation,  but  those  whose  experience  is  of  opposite 
conditions  may  reckon  this  estimate  to  be  moderate. 

In  the  preliminary  stages  of  a  project,  information  concerning 
the  needs  of  agriculture,  so  far  as  irrigation  is  concerned,  will 
be  sought  after  by  consulting  the  local  farmers.  But  it  must 
not  be  assumed  that  the  cultivator's  judgment  as  to  what  is  best 
for  his  crops  is  infallible,  when  the  conditions  of  farming, 
introduced  by  irrigation,  are  outside  the  limits  of  his  experience. 
When  the  quantity  of  water  obtainable  is  abundant  and  the 
farmer  does  not  pay  for  it  according  to  the  actual  quantity 
taken,  he  is  apt  to  over-water  his  crop,  and  has  to  be  taught  by 
experience  that,  though  water  is  a  good  thing,  a  crop  may  have 
too  much  of  it.  Especially  is  this  the  case  if  a  deficiency  in 
the  supply  of  water  has  been  the  normal  condition  under  which 
crops  have  had  to  be  raised  previous  to  the  introduction  of 
irrigation.  Cotton  cultivation,  for  instance,  appears  to  suffer 
from  a  too  liberal  supply  of  water.  It  was  said  some  years 
ago,  with  reference  to  the  cotton  crop  in  Egypt,  that  the 
shorter  the  water  supply  the  greater  the  yield  of  the  crop. 
This  generalisation,  based  on  the  figures  of  a  few  years  only, 
could  obviously  be  discredited  by  a  rcductio  ad  absurdwn.  But 
the  figures  of  the  cotton  crop  of  Egypt  for  late  years  seem  to 
show  that  over-watering  is  practised  when  the  opportunity 
offers,  and  that  over- watering  is  followed  by  a  decrease  in  yield. 
The  total  yield  for  all  Egypt  in  1897  was  6,513,444  cwt.;  in 
1899,  6,432,776  ;  in  1901,  6,369,911.  For  the  intermediate  years 
it  was  less.  In  1903  the  Assuan  reservoir  was  filled  and  drawn 
upon  for  the  first  time,  and  there  was  a  considerable  extension 
of  the  area  put  under  cotton  in  1903  and  1904.  Nevertheless, 
in  both  those  years  the  yield  was  less  than  it  had  been  before 
1903.  There  was  no  advance  on  the  record  figure  of  1897  in 
spite  of  the  extension  of  the  area  under  crop.  The  official 
reports  of  the  Irrigation  Department  of  Egypt  state  that  the 
water  supply  of  1903  and  1904  "  was  everywhere  plentiful ;  too 
plentiful  perhaps."  It  is  possible  that,  as  the  area  increases 


252  IRRIGATION. 

under  the  stimulus  of  the  increased  supply  and  the  water  allow- 
ance per  acre  becomes  less,  the  yield  per  acre  may  again  rise  to 
as  high  a  figure  as  it  had  reached  before  the  Assuan  darn  came 
into  operation.  If  so,  the  record  total  yield  of  Egypt  of 
1897  will  then  be  surpassed  by  a  considerable  figure.  Now,  in 
the  Irrigation  Report  for  1904,  it  is  stated  that  the  "duty" 
that  was  got  out  of  the  water  in  the  summer  of  1904  was 
"  probably  the  lowest  ever  recorded,"  and  that  there  had  not 
been  such  a  good  summer  supply  in  the  river  since  1899.  The 
moral  of  this  would  seem  to  be  that,  if  a  given  quantity  of 
water  is  best  suited  to  any  crop,  it  is  a  mistake  to  give  more 
than  that  quantity ;  and  the  irrigation  officers  would  be  acting 
in  the  interests  of  the  farmers  if  they  were  to  make  excessive 
watering  impossible  by  withholding  the  super-abundant  supply, 
even  if  so  doing  necessitated  running  water  to  waste.1  But  to 
run  water  to  waste  when  cultivators  are  demanding  more,  even 
though  giving  way  to  the  demand  would  be  prejudicial  to  their 
interests,  is  an  unpopular  thing  to  do,  and  is  a  difficult  policy 
to  carry  out  in  the  face  of  an  almost  universal  belief  that,  in  a 
conflict  of  opinions  between  the  irrigation  officer  and  the 
agriculturist  over  a  question  concerning  crop  requirements,  the 
former  must  necessarily  be  in  the  wrong.  A  good  irrigation 
engineer  will  be  all  the  better  for  a  sound  knowledge  of  the 
agricultural  conditions  and  needs  of  the  district  which  is  or  will 
be  affected  by  the  canal  system  under  his  control,  and  it  is  part 
of  his  duty  to  acquire  such  knowledge,  so  as  to  enable  him 
to  apply  his  professional  ability  to  the  best  advantage. 

The  limitation  of  the  water  supply,  in  a  healthy  system  of 
canals,  to  the  real  requirements  of  the  crops,  has  a  further 
advantage  beyond  the  prevention  of  over-watering.  It  also  pro- 
tects the  drains,  which  have  to  carry  off  the  excess,  from  being 
over- worked  to  such  an  extent  that  they  cannot  perform  their 
part  efficiently.  When  the  excess  that  reaches  them  is  reason- 
able in  quantity  and  no  more  than  they  have  been  designed  to 
1  See  Note  10,  Appendix  IV. 


AGRICULTURAL  OPERATIONS  AND  RECLAMATION  WORKS.      253 

carry  off,  the  evils  of  water-logging  and  stagnation  are  avoided. 
It  has  been  said  that  irrigation  water,  to  be  entirely  beneficial, 
must  reach  everywhere,  but  remain  nowhere.  The  putting  into 
practice  of  this  theoretical  formula  is  most  difficult  in  the  case 
of  the  low-lying  lands  of  flat  slope  which  lie  along  the  sea-ward 
margin  of  most  deltas.  Such  lands  are  often  salted,  and  the 
problem  of  their  reclamation  is,  therefore,  not  solved  by  merely 
getting  rid  of  the  water  that  covers  them  permanently  or  occa- 
sionally, and  by  draining  them ;  but  the  salt  that  makes  the 
land  infertile  must  be  washed  out  of  it.  The  land  surface  is  so 
little  above  sea-level  that  drainage  by  gravitation,  or  free  flow, 
is  an  impossibility.  The  water  has  to  be  got  rid  of  by  pumping. 
There  are  wide  stretches  of  low-lying  level  lands,  at  present 
barren  wastes  and  marshes,  lying  unreclaimed  along  the  north 
margin  of  the  delta  of  Egypt.  There  is  so  much  else  in  Egypt 
that  it  pays  better  to  reclaim  or  develop,  that  it  will  be  many 
years  yet  before  cultivation  extends  northwards  from  its  present 
limit  as  far  as  the  borders  of  the  sea. 

The  reclamation  of  such  lands,  however,  is  a  possibility. 
Holland,  and  the  valley  of  the  Po  in  Italy,  furnish  instances  of 
successful  reclamation.  The  first  thing  to  do  is  to  get  rid  of 
the  salt  in  the  soil.  If  the  flood  water  of  the  river  can  be  made 
to  flow  freely  over  the  surface,  some  of  the  salt  will  be  carried 
away  in  the  water.  But  it  is  not  often  possible  to  secure  surface 
washings  sufficiently  copious  or  prolonged  to  remove  the  salt 
for  more  than  a  comparatively  shallow  depth.  The  salt  below 
is  more  effectually  got  rid  of  by  a  system  of  deep  drains  into 
which  the  water  finds  its  way  by  downward  percolation  through 
the  soil,  carrying  the  salt  with  it.  These  operations  of  surface 
washings  and  subsoil  drainage  can  be  effected  in  the  following 
way.  The  land  to  be  reclaimed  would  be  surrounded  by  a 
bank  to  exclude  all  water  other  than  that  purposely  admitted. 
The  earth  to  form  the  bank  would  be  obtained  from  a  ditch 
dug  along  the  inside  of  it  to  a  regular  section  to  serve  as  a 
collecting  drain.  At  the  higher  end  of  this  enclosure,  at  the  most 


254  IRRIGATION. 

convenient  point,  a  head  sluice  on  tfte  feeder  canal  would  admit 
water  under  control.  At  either  end  of  the  lower  side  escapes 
would  provide  exits  for  the  water  of  surface  washings.  At  the 
lowest  point  of  the  enclosure,  or  at  the  most  convenient  point 
on  the  interior  drain,  a  pump  to  lift  the  drainage  water  would 
be  set  up.  Irrigating  channels  in  connection  with  the  head 
sluice  would  distribute  the  water  admitted  over  the  enclosed 
area,  and  drains,  alternating  with  the  irrigating  channels,  would 
lead  to  the  pumping  station.  The  first  operation  of  surface 
washing  would  then  be  conducted,  during  the  season  when 
water  was  plentiful,  by  opening  the  head-sluice  and  keeping  the 
escapes  closed  until  the  whole  of  the  enclosed  area  was  covered 
with  a  sheet  of  water.  As  soon  as  that  had  occurred,  the 
escapes  would  be  opened  to  the  extent  necessary  to  discharge  as 
much  as  was  being  admitted  through  the  head  sluice,  so  that 
the  water  level  in  the  enclosure  might  remain  constant.  When 
it  was  no  longer  possible  to  continue  the  supply,  the  head  sluice 
would  be  closed,  the  escapes  be  fully  opened,  and  the  water  run 
off  to  as  low  a  level  as  it  would  go.  When  it  ceased  to  flow,  the 
escapes  would  be  closed  to  prevent  a  back  flow,  and  the  pumps 
would  lift  the  remaining  water  into  a  discharging  channel  outside 
the  enclosure,  which  would  carry  it  away.  The  drain  along  the 
inside  of  the  enclosing  bank  and  the  drains  all  over  the  area,  alter- 
nating with  irrigating  channels,  would  lead  all  excess  water  to 
the  pumping  station  and  keep  the  saturation  level  low.  The  head- 
sluice  would  admit  the  supply  required  for  the  irrigation  of  the 
crops  or  for  other  operations,  and  the  irrigation  channels  would 
distribute  it.  The  surface  washing  would  probably  have  to  be 
repeated  more  than  once  before  the  soil  would  become  cultivable. 
But  meanwhile,  after  a  surface  washing,  supposing  water  is 
available,  the  system  of  subsoil  drainage  would  be  brought 
into  play  to  do  its  part  in  getting  rid  of  the  salt.  The  method 
of  proceeding  consists  in  surrounding  plots  of  land  of  con- 
venient dimensions  by  ridges,  and  filling  the  enclosed  plots  with 
water  of,  say,  one  foot  in  depth.  The  water  in  the  deep  drains 


AGRICULTURAL  OPERATIONS  AND   RECLAMATION  WORKS.      255 

alongside  the  plots  is  kept  low  by  the  pumps.  The  watei 
covering  the  plots  sinks  into  the  ground  and  percolates  down- 
wards and  outwards  to  the  drains,  carrying  salt  with  it.  The 
plots  are  filled  again  and  again,  and  the  process  repeated  till  the 
soil  is  sufficiently  free  of  salt  to  be  cultivable. 

Finally,  to  enrich  the  soil,  the  turbid  flood  water  should  be 
admitted  and  kept  standing  in  the  enclosed  area  long  enough 
to  throw  down  its  fertilising  matter,  and  be  then  run  off.  It  is 
well  to  make  provision,  in  the  arrangements  for  the  reclamation 
of  these  low  lands,  for  periodical  washings  every  third  year  or 
so,  as  their  tendency  is  to  return  to  their  original  salted  con- 
dition ;  and  it  is  therefore  necessary  to  adopt  effective  measures 
to  counteract  the  tendency. 

Whether  it  is  worth  while  to  incur  the  expenditure  of  reclaim- 
ing land  which,  it  might  be  urged,  Nature  has  not  intended  for 
cultivation,  depends  upon  many  things.  It  has  been  argued 
that,  inasmuch  as  it  pays  to  lift  water  for  raising  crops  by 
irrigation  on  high  lands  which  get  free  flow  drainage,  it  should 
pay  to  bring  land  under  cultivation  by  lifting  the  drainage  water 
that  runs  off  land  which  enjoys  free  flow  irrigation,  because  the 
amount  drained  off  irrigated  land  must  of  necessity  be  less  than 
the  amount  supplied  for  its  irrigation.  This  argument  would  be 
conclusive  if  the  yield  of  the  crops  in  both  cases  were  the  same. 
But  that  is  often  by  no  means  the  case,  the  low  lands  after 
reclamation  being  generally  poor  in  quality  in  comparison  with 
the  high  lands.  In  Egypt  the  high  lands  near  the  head  of  the 
delta,  for  the  irrigation  of  which  water  has  to  be  pumped,  yield 
twice  as  much  cotton  per  acre  as  the  low  lands  in  the  north  of 
the  delta  near  the  sea. 

There  is  another  difficulty  which  must  not  be  lost  sight  of  in 
considering  the  pros  and  cons,  of  any  reclamation  scheme.  There 
would  generally  be  a  want  of  hands  to  carry  out  the  operations 
of  reclamation  and  farming,  as  no  villages  or  habitations  would 
be  found  on  waste  lands  that  produce  nothing.  The  population 
would  have  to  be  brought  from  elsewhere  and  given  inducements 


256  IRRIGATION. 

to  settle.  Means  of  transport  would  also  have  to  be  provided 
for  the  conveyance  of  the  produce  of  the  land  to  a  market  where 
it  could  be  sold.  In  Chapter  I.  it  has  already  been  told  how,  in 
India,  a  new  population  of  1,000,000  founded  homesteads  on 
some  2,000,000  acres  of  waste  land  which  had  been  reclaimed  to 
cultivation  by  the  waters  of  the  Lower  Chenab  Canal.  But  it  is 
not  all  countries  that  have  such  human  reserves  as  India  has  to 
draw  upon  ;  and  want  of  population  will  often  necessitate  the 
postponement  of  reclamation  schemes. 

Another  important  consideration  in  estimating  the  financial 
prospects  of  any  scheme  involving  pumping  on  any  considerable 
scale  is  the  cost  of  the  fuel  required  for  generating  power  by 
steam,  electricity  or  other  means,  whether  the  object  is  irrigation 
or  drainage.     For  fuel  is  the  most  important  item  in  the  pump- 
ing expenditure.     Large  pumping  stations  work  more  economi- 
cally than  small  ones,  the  establishment  and  other  charges  being 
relatively  less  in  a  large  than  in  a  small  installation.     There  is  a 
large  pumping  station  at  Mex  (Plate  IX.),  near  Alexandria,  which 
works  in  the  interests  of  drainage.     A  large  area  of  the  western 
delta  of  Egypt  drains  into  Lake  Mareotis,  and  the  efficiency  of 
the  drains  depends  on  the  control  of  the  surface  level  of  the  lake. 
It  is  the  business  of  the  Mex  pumps,  therefore,  to  keep  the  lake 
surface  from  rising  above  a  certain  fixed  level.     The  pumping 
station  consists  of  two  48  inch  centrifugals  with  horizontal  shafts, 
and  5  centrifugals  with  vertical  shafts  (shown  under  erection  in 
PlatelX.)  worked  by  seven  engines  of  anaggregateof  1,500  W.H. P. 
It  is  capable  of  lifting  a  maximum  of  35  cubic  metres  (1,227 
cubic   feet)    per  second.     In   1918   the   pumps,    working   for 
286  days,  lifted  624,000,000  cubic  metres  of  water  at  a  total 
cost  of  about  £50,000.     The  price  of  fuel  was  in  that  year 
abnormally  high  on  account  of  the  war. 

A  much  smaller  pumping  station  at  Kassassin,  also  for 
drainage  purposes,  lifts  water  2j  to  3  metres.  In  1918  the  cost 
of  the  pumping  was  at  the  rate  of  nearly  £200  per  million  cubic 
metres — an  abnormal  rate,  due  to  war  conditions.  This 


AGRICULTURAL  OPERATIONS  AND  RECLAMATION  WORKS.      257 

station  is  capable  of  lifting  5|  cubic  metres  (about  200  cubic 
feet)  a  second.  It  is  composed  of  five  engines  driving  six 
centrifugal  pumps  with  horizontal  shafts.  With  smaller 
stations  the  cost  per  unit  of  volume  pumped  would  be  consider- 
ably higher.  Sir  William  Willcocks,  nevertheless,  recommends 
small  pumping  stations  in  the  case  of  reclamation  work.  In 
his  lecture  on  Irrigation  on  the  Tigris,  delivered  in  Cairo  on 
March  25th,  1903,  he  expresses  his  opinion  in  the  following 
words- — "The  important  point  is,  that  numbers  of  small  pumps 
should  be  placed  on  the  banks  of  the  main  drains,  draining 
small  areas  and  discharging  direct  into  the  mains.  Such 
pumps  should  be  actuated  by  one  central  electric  station  for 
reasons  of  economy.  The  results  of  such  drainage  would  be 
immediately  apparent.  The  early  failures  of  large  reclamation 
works  were  nearly  always  due  to  the  extensive  areas  drained  by 
single  installations."  He  considers  the  most  economical  area 
to  drain  with  one  pump  to  be  2,500  acres. 

The  new  departure  of  the  Irrigation  Service  of  India  in  adopt- 
ing a  pumping  scheme  for  the  irrigation  of  the  Divi  Island,  on 
the  Kistna  river  in  Madras,  has  already  been  referred  to  at  tne 
end  of  Chapter  VI.  As  was  there  stated,  the  pumping  station 
consists  of  eight  1 60 -brake-horse-power  Diesel  oil  engines,  each 
actuating  a  Gwynne  centrifugal  pump  with  a  39-inch  diameter 
discharge  pipe.  The  pumps  lift  water  10  to  12  feet  for  the 
irrigation- of  50,000  acres.  The  estimated  cost  of  the  first 
installation  was,  in  ro;*nd  figures,  £35,000.  The  quantity  of 
water  lifted  is  500  cubic  feet  a  second.  The  fuel  used  is  oil. 
The  estimated  annual  expenditure,  with  a  pumping  season  of 
4  months  continuous  work  lifting  500  cubic  feet  a  second,  was 
£7,384  for  a  total  quantity  lifted  of  5,184,000,000  cubic  feet. 
This  gives  a  rate  of  £i  8s.  6d.  per  1,000,000  cubic  feet,  or  £50  per 
1,000,000  cubic  metres,  lifted.1 

1  The  Government  of  India  Report  for  1916  17  states:  "Although  it  has 
only  been  completed  for  somewhat  over  three  years,  a  net  return  upon  capital 
of  3£  per  cent,  is  already  being  realised." 

I.  S 


CHAPTER   XIII. 

NAVIGATION. 

THE  waterway  provided  by  the  construction  of  an  irrigation 
canal  is  often  adapted  to  navigation.  Whether  it  is  desirable 
to  make  one  and  the  same  canal  serve  two  masters  is  a  question 
that  has  been  much  disputed  by  the  canal  engineers  of  India, 
ever  since  Sir  Arthur  Cotton,  in  1854,  preached  the  gospel  of 
navigation.  The  question  does  not  seem  to  be  finally  settled 
yet.  It  is  probable  that  the  combination  of  irrigation  and 
navigation  is  desirable  in  some  cases  and  not  in  others,  but 
that  it  is  not  so  generally  desirable  as  the  early  enthusiasts  for 
navigation  asserted.  In  a  paper  on  the  Navigable  Waterways 
of  India,  read  on  Feb.  I5th,  1906,  before  the  Indian  Section  of 
the  Society  of  Arts  by  Mr.  R.  B.  Buckley,  C.S.I.,  it  was  shown 
that,  out  of  a  total  length  of  11,858  miles  of  irrigation  canals, 
in  India,  2,778  miles  were  navigable.  Judged  by  the  receipts 
credited  under  the  head  of  navigation,  it  cannot  be  said  that,  as 
a  rule,  there  has  been  a  satisfactory  return  for  the  expenditure 
incurred  in  adapting  irrigation  canals  to  navigation.  Mr. 
Buckley  mentions  the  Godavery  system  in  Madras,  and  the 
Orissa  and  Midnapore  systems  in  Bengal,  as  the  canals  in 
which  navigation  has  been  most  successfully  combined  with 
irrigation. 

An  irrigation  canal  should  follow  the  line  which  is  best 
suited  to  it  as  an  irrigating  channel ;  a  navigation  canal  should 
connect  the  producing  areas  with  the  markets,  where  the 
products  are  to  be  disposed  of,  by  the  most  direct  line  that  may 
be  economically  possible.  It  is  not  likely  that  the  two  lines 
would  be  identical,  though  occasionally  they  might  ba  I* 


NAVIGATION.  259 

irrigation  and  navigation  are  to  be  partners  in  one  business 
there  must  be  compromises  arranged,  since  what  is  best  for  the 
one  is  not   so   for   the  other.     The   principles   on   which    an 
irrigation  canal  should  be  designed  have  been  pointed  out  in 
Chapter  VIII.     It  was  shown  that  the  velocity  of  flow  should 
be  such  that  there  would  be  neither  deposit  of  silt  nor  scour  of 
the  bed  or  banks.     A  velocity  complying  with  these  conditions 
might  very  easily  be  too  high  for  the  convenience  of  naviga- 
tion, which  would  be  better  suited  by  a  sluggish  current  or  no 
current  at  all.     It  has  also  been  explained  in  Chapter  X.  that  it 
is  desirable  for  economical  distribution  of  water  in  irrigation  to 
regulate  the  discharges  in  the  canals  so  that  periods   of  low 
supply  should  alternate  with  periods  of  high  supply.     Such  a 
fluctuating  system  would  be  very  disconcerting  to  boats,  at  any 
rate  when  fully  laden.     There  are  besides  other  respects   in 
which  irrigation  and  navigation  requirements  conflict  when  the 
same  canal  has  to  satisfy  both.     Nevertheless  it  is  sometimes 
advantageous,  all  things  considered,  to  make  an  irrigation  canal 
navigable,  so  that  it  may  not  only  furnish  the  means  for  raising 
products  of  the  soil,  but  may  also  offer  facilities  for  transporting 
the  same  products  to   market.     The    importance   of    inland 
waterways  as  affording  a  cheap  method  of  transport  for  bulky 
goods  of  all  descriptions  has  received  practical  recognition  in 
France,  Belgium,  Germany  and  America  to  the  great  advantage 
of  their  trade.     But   the   canals   which   form    part   of  their 
schemes  of  inland  waterways  are,  for  the  most  part,  designed 
exclusively  for  navigation  purposes,  and  are  unconnected  with 
irrigation.     It  is  in  India  and  Egypt  that  examples  of  canals 
serving  both  objects  will  be  found. 

A  navigable  canal,  or  navigable  system  of  canals,  must,  in 
the  first  place,  have  uniformity  of  gauge,  that  is,  the  locks 
should  all  have  the  same  dimensions  and  the  canals  an  uniform 
cross  section,  so  that  the  largest  sized  craft  that  can  navigate 
any  part  of  the  system  can  navigate  it  throughout. 

When  an  irrigation  canal  has  to  be  adapted  to  navigation,  it 

S  2 


260  IRRIGATION, 

is  necessary  to  reduce  the  velocity  of  flow  so  that  it  may  not 
exceed  from  ij  to  2  feet  a  second.  As  in  most  cases,  when 
this  condition  is  complied  with,  the  water-surface  slope  of  the 
canal  will  be  less  than  that  of  the  land  surface,  it  will  be 
necessary  to  provide  falls  at  intervals  along  the  canal,  so  that 
when  the  water  level  has  reached  the  maximum  height  above 
country  level  that  is  convenient,  it  may  be  dropped  down 
within  soil.  At  each  point  where  a  fall  is  necessary,  a  lock 
must  be  built  to  give  passage  to  boats  between  the  upper  and 
lower  reaches. 

There  are  three  different  positions  in  which  the  lock  may  be 
placed  with  reference  to  the  fall  with  which  it  is  associated. 
The  fall  may  be  placed  on  the  main  canal,  and  the  lock  on 
a  side  channel  taking  off  from  the  canal  above  the  fall  and 
rejoining  it  below.  Or  the  lock  may  be  on  a  navigable  channel 
dug  on  the  direct  line  of  the  canal  axis,  while  the  fall  is  placed 
on  the  main  channel  which  is  diverted  round  the  lock  on  a 
curved  alignment.  In  both  these  cases  the  fall  and  lock  are 
usually  built  in  such  positions  that  the  roadway  over  the  two  may 
be  in  one  straight  line.  The  third  plan  is  to  make  a  combined 
work  of  lock  and  fall,  and  to  have  no  side  channel.  The 
advantage  of  the  last  arrangement  is  that  the  entrance  to  the 
lock  is  kept  clear  of  silt ;  the  disadvantage  is,  that  when  the 
discharge  over  the  fall  is  considerable,  the  draw  of  the  current 
may  make  it  difficult,  or  even  dangerous,  for  boats  to  enter  the 
lock.  On  the  other  hand,  the  disadvantage  of  placing  the  lock 
on  a  separate  channel  from  the  fall  is  that  the  channel  above 
and  below  the  lock  has  a  tendency  to  silt  up,  and,  if  not  kept 
clear  by  dredging  or  otherwise,  boats  may  find  it  not  merely 
difficult,  but  impossible  to  enter  the  lock.  But  a  lock  so 
placed  has  the  advantage  that  the  entrance  and  exit  of  boats 
is  effected  in  still  water. 

Sometimes,  instead  of  a  fall  or  weir  to  hold  up  the  water 
with  the  object  of  reducing  the  velocity  of  flow  or  of  producing 
a  sufficient  depth  for  boats  in  the  reach  above,  a  regulator  is 


NAVIGATION.  26 1 

necessary  for  the  purpose  of  raising  or  lowering  the  water  level 
to  suit  the  needs  of  irrigation.  Whenever  the  regulator  may 
be  used  to  hold  the  water  in  the  upper  reach  at  a  higher  level 
than  that  in  the  lower  reach,  the  lock  comes  into  action  for  the 
passage  of  boats ;  but  when  the  regulator  is  fully  open,  both 
pairs  of  lock  gates  also  can  be  opened,  and  boats  be  passed 
freely  without  the  necessity  of  bringing  the  locking  arrangements 
into  operation. 

The  chamber  of  a  lock  may  be  looked  upon  as  a  very  short 
reach  of  canal  with  regulators  at  the  upper  and  lower  ends,  by 
means  of  which  the  water  level  between  them  can  be  raised 
and  lowered  at  will  to  the  levels  of  the  reaches  above  and 
below  respectively,  so  that  boats  may  be  raised  or  lowered 
from  one  to  the  other.  The  pairs  of  lock  gates  with  their  face 
sluices,  and  the  filling  and  emptying  side  sluices,  perform  the 
office  of  regulators.  In  fact,  it  sometimes  happens  that  a 
reach  of  a  canal  is  treated  as  a  lock.  If  the  discharge  of  an 
irrigation  canal,  which  is  navigable,  falls  below  the  normal 
minimum  contemplated  when  grading  the  canal,  or  if  the  bed 
is  raised  by  silt  deposit,  boats  often  run  aground  at  the  upper 
end  of  a  reach,  or  in  the  down-stream  exit  channel  of  the  lock, 
and  are  either  unable  to  enter  the  lock  if  ascending  the  canal, 
or  to  leave  the  lock  if  descending.  It  then  becomes  necessary 
to  hold  up  the  water  by  regulation  at  the  lower  end  of  the  reach, 
so  that  there  may  be  depth  of  water  enough  for  boats  to  pass 
in  and  out  of  the  lock  at  the  upper  end  of  the  reach.  A  very 
large  lock  might  be  economically  made  on  a  canal  by  separating 
the  two  pairs  of  gates  and  their  sluices  into  two  distinct  works 
with  the  chamber  between  them  formed  by  a  convenient  length 
of  the  earthen  channel  of  the  canal.  In  harbours  the  lock 
chamber  is  sometimes  developed  into  a  basin  of  considerable 
area.  But  the  dimensions  of  canal  lock  chambers  are  limited 
for  reasons  other  than  economy  of  construction.  Economy  of 
water  in  the  working  of  a  canal  is  often  a  more  important 
consideration  than  economy  in  the  first  cost  of  construction. 


262  IRRIGATION. 

Every  time  boats  are  passed  through  a  lock,  a  volume  of  water 
equal  to  that  required  to  raise  the  level  in  the  lock  chamber 
from  that  of  the  lower  to  the  higher  reach  has  to  be  passed 
forward  from  above  to  below  the  lock.  In  irrigation  canals — in 
their  upper  reaches  at  any  rate — this  is  not  a  serious  matter,  as 
the  passing  forward  of  water  is  always  required  to  feed  the 
distributing  canals.  But  in  purely  navigation  canals,  where 
the  supply  of  water  for  keeping  the  reaches  full  is  extremely 
limited,  economy  of  the  available  water  supply  may  become  a 
question  of  first  importance,  calling  for  devices  such  as  lifts 
and  inclines  to  promote  economy.  Another  matter  affecting 
the  dimensions  of  lock  chambers  is  the  value  of  time.  Given 
the  same  discharging  capacity  of  sluices,  a  large  lock  naturally 
tikes  longer  to  fill  than  a  small  one,  and  the  time  taken  by  the 
canal  traffic  to  pass  from  one  reach  to  the  other  would  be 
greater  with  the  large  lock  ;  and  unnecessarily  greater,  whenever 
the  lock  space  is  only  purtially  utilised  by  passing  boats  or 
barges.  The  dimensions  of  the  lock  should  therefore  be  deter- 
mined by  the  traffic  which  may  be  expected  to  use  the  canal, 
and  should  not  be  excessive. 

The  most  common  form  of  lock  gates  is  that  in  which  a  pair 
of  gates  meet  at  an  angle  and  are  pressed  against  each  other 
and  against  a  bed  sill  by  the  head  of  water  bearing  against 
them.  The  gates  may  be  of  wood  or  iron,  .and  the  sill  faces  of 
wood,  iron  or  masonry ;  but  wood  is  not  used  in  important 
locks.  f  A  less  common  form  is  the  single  leaf  gate,  which  spans 
the  lock  chamber  from  side  to  side  and  bears  against  vertical 
faces  in  the  sides  of  the  lock.  To  open  the  lock,  the  gate  is 
withdrawn  sideways  into  a  recess  buiit  at  right  angles  to  the 
lock  chamber.  In  the  locks  of  the  Assuan  dam  such  a  single 
leaf  gate  has  been  the  form  adopted.  It  is  hung  from  above  by 
seven  pairs  of  sling  rods,  attached  to  two  sets  of  free  rollers, 
which  are  free  to  move  along  two  bascule  girders  spanning  the 
lock.  The  gate  is  withdrawn  into  a  recess  in  the  side  of  the  lock 
by  the  movement  of  its  supporting  rollers  along  the  bascule 


NAVIGATION.  263 

girder.  When  the  gate  is  safely  housed  in  its  recess  beyond 
the  pivoting  end  of  the  bascule  girder,  the  latter  is  raised  into 
a  vertical  position  to  free  the  passage  way  for  vessels  using  the 
lock.  The  opening  and  closing  of  the  valves  of  the  lock  gates, 
the  moving  of  the  gate  backwards  and  forwards,  and  the  lifting 
of  the  bascule  girder,  are  all  effected  by  hydraulic  power.  The 
system  adopted  at  Assuan  has  proved  expensive,  and  is  not 
likely  to  be  imitated  for  gates  of  smaller  dimensions  than  those 
of  the  Assuan  dam  locks. 

In  some  cases  the  single  leaf  gate,  instead  of  being  suspended 
from  above,  rests  upon  the  floor  of  the  lock ;  and,  to  facilitate 
its  movement  backwards  and  forwards  from  and  to  the  recess, 
arrangements  are  made  for  floating  it. 

A  lock  has,  in  certain  situations,  to  be  furnished  with  gates  to 
act  when  the  normal  head  is  reversed.  Such  conditions  would 
exist  where  a  lock  constituted  the  connecting  work  between 
the  terminal  reach  of  a  canal  and  a  tidal  harbour.  In  such  a 
case  the  gates  would  have  to  be  duplicated,  so  that  the  levels 
in  the  lock  might  be  controlled  on  whichever  side  the  higher 
water  might  be. 

As  time  is  often  a  serious  consideration  in  the  transport  of 
goods,  and  as  every  lock  on  a  navigable  line  is  a  source  of 
delay,  it  is  important  to  arrange  for  passing  boats  through 
locks  as  quickly  as  possible.  To  this  end  means  must  be  pro- 
vided for  rapidly  filling  and  emptying  the  lock  chamber.  The 
Manual  on  Irrigation  Works  of  the  College  of  Engineering  in 
Madras  lays  it  down  that  "  locks  should  be  capable  of  being 
filled  or  emptied  in  three  minutes."  The  filling  and  emptying 
is  effected  by  sluices  in  the  lock  gates,  often  assisted  by  sluice 
ways  built  round  the  gates  in  the  thickness  of  the  lock  walls. 
The  discharging  capacity  of  the  sluices  must  be  sufficient  to 
effect  the  filling  or  emptying  of  the  lock  within  the  maximum 
period  permissible.  The  filling  sluice-way  in  the  lock  walls  is 
sometimes  carried  along  the  whole  length  of  the  chamber,  and 
is  given  several  outlets  into  it  at  intervals  along  its  length  with 


264  IRRIGATION. 

the  object  of  diminishing  the  back-waters  and  eddies  which 
are  produced,  to  the  inconvenience  and  sometimes  danger  of 
boats,  when  the  inflow  is  concentrated  at  one  or  two  points 
only. 

But  the  most  important  matter  affecting  the  disposition  of 
the  sluices  is  the  tendency  of  silt  to  deposit  against  the  up- 
stream face  of  the  gates,  creating  thereby  an  impediment  to 
their  opening.  To  counteract  this  tendency,  sluices  are  fitted 
in  the  face  of  the  lock  gates  at  as  low  a  level  as  the  design  of 
the  gates  permits.  The  inlets  of  the  side  sluices  in  the  masonry 
of  the  lock  walls  are  also  so  disposed  as  to  create  a  scouring 
action  over  the  floor  immediately  up  stream  of  the  gates.  In 
the  case  of  a  lock  fitted  with  the  ordinary  pair  of  gates  meeting 
at  an  angle,  the  inlet  openings  to  the  sluice  way  are  made  in 
the  face  of  the  recess  in  which  the  gate  lies  when  fully  open ; 
and  their  sills  are  placed  on  a  level  with  the  floor  over  which 
the  gates  move.  In  the  Zifta  barrage  lock  there  are  three 
such  inlets  in  each  gate  recess  communicating  with  one  united 
sluiceway,  which  in  the  case  of  the  upper  gate  sluices  (Fig.  66) 
leads  to  an  outlet  into  the  lock  chamber,  and  in  the  case  of  the 
lower  gate  sluices  into  the  channel  below  the  lock.  Difficulties 
arising  from  silt  deposit  above  and  within  locks  are  especially 
met  with  in  the  case  of  locks  at  the  off-take  of  a  canal  from  a 
muddy  river,  and  on  irrigation  canals  adapted  to  navigation, 
which  carry  silt  laden  water  for  the  sake  of  the  cultivation 
served  by  them.  An  intelligent  and  experienced  lock-keeper 
in  charge  of  a  lock  with  well  designed  sluices  can  do  much, 
by  a  skilful  manipulation  of  the  sluice  gates,  to  minimise  the 
inconveniences  arising  from  silt  deposit. 

The  chamber  walls  of  a  lock  when  empty  act  as  retaining 
walls  to  support  the  earth  backing.  The  dimensions,  however, 
of  an  ordinary  retaining  wall  are  considered  insufficient  for  a 
lock  wall,  as  the  rapid  emptying  of  the  lock  chamber  brings 
pressures  to  bear  on  the  wall  which  are  somewhat  in  the  nature 
of  those  due  to  a  live  load.  If  the  wall  has  an  interior  vertical 


NAVIGATION. 


265 


face,  a  thickness  of  3  feet  at  the  top,  and  a  hack  batter  of  i  in 
4  obtained  by  offsets,  will  give  a  profile  that  is  suitable  in  most 
cases.  The  Zifta  barrage  lock  (Fig.  67)  furnishes  an  example 
of  a  lock  with  interior  vertical  faces ;  the  Assuan  lock  (Fig.  68) 
that  of  a  lock  having  interior  faces  built  with  a  batter.  Though 
the  latter  gives  a  better  disposition  of  the  material  for  resisting 
the  pressure  of  the  backing,  there  is,  in  some  cases,  a  serious 
objection  to  diminishing  the  width  of  the  lock  chamber  between 
high  water  and  low  water  levels.  For  if,  when  the  water  in  a 

ZIFTA    BARRAGE    LOCK 


1fc^ 


Scale 

30  50 


100 

j     Feet 


FIG    66 


FIG     67 


PLAN    OF  SIDE    SLUICES 


I 

(= 

CNAMI 

A 

i 

SATS    \ 

| 

r 

-^ 

\<     i 

v 

Sfj)n  SLirrcas 

j  —  i  1 

f 

32}-  - 


I 


m 


'/*//.-, 


CD 


a  a.  Wells   of  Sluice    Gates 


CD 


lock  with  interior  face  batter  is  at  the  level  of  the  upper  reach, 
boats  are  admitted  in  such  numbers  that  they  completely  fill  the 
lock  from  side  to  side,  they  will  do  more  than  fill  it  when  the 
water  is  lowered,  and  may  be  capsized  by  one  side  being  held 
up  against  the  lock  wall  while  the  other  sinks  with  the  water. 

As  a  rule,  from  15  to  16  feet  is  about  the  maximum  difference 
of  level  that  is  overcome  by  one  lock.  If  the  difference  is 
greater,  the  change  of  level  is  effected  by  two  locks,  a  double 
lock,  or  a  flight  or  ladder  of  locks.  The  total  drop  at  the 
Assuan  dam,  from  the  high  water  level  in  the  reservoir  above 
the  dam  to  the  river  low  water  level  below  it,  is  90  feet.  To 


266 


IRRIGATION. 


pass  boats,  a  five-fold  flight  of  locks  has  been  provided  on  one 
flank  of  the  dam. 

It  is  a  not  uncommon  thing  for  a  longitudinal  crack  to 
appear  in  the  floor  of  a  lock  under  construction,  when  the  walls 
have  reached  a  certain  height.  This  occurs  when  the  soil  on 
which  the  lock  is  built  is  compressible,  and  the  pressure  over 


UPSTREAM  LOCK  ASSUAN  DAM 

LT....T 


Scale 

T    i    T 


to 

H   Feet 


FIG    68 


the  area  of  the  foundations  is  unequally  distributed,  producing 
uneven  settlement.  If  the  centre  of  pressure  of  the  weight  of 
the  wall  and  its  earth  backing  falls  so  far  behind  the  centre 
of  the  figure  of  the  base  as  to  be  beyond  the  safe  limit,  the 
inequality  that  produces  settlement  is  established.  But  this 
result  can  be  avoided  by  giving  the  base  a  considerable  width 
and  lightening  the  back  of  the  walls  by  a  distribution  of  void 
spaces  in  the  thickness  of  the  masonry. 


APPENDIX    I. 


WEIGHTS  AND  MEASURES. 

WEIGHTS. 

i  cubic  foot  of  water  weighs  62$  Ibs. 
i  cubic  metre  of  water  weighs  i  ton  (very  nearly), 
i  kilogramme  =  2*2046  Ibs. 
i  Ib.  =  '4536  kilogramme. 

i  Ib.  per  square  inch  =  '0703  kilogramme  per  square  centimetre, 
i  kilogramme  per  square  centimetre  =  14-22  Ibs.  per  square  iocfi 

LINEAL  MEASURES. 
i  metre  =  3*2809  feet, 
i  foot  ='3048  metre. 
5  miles  =  8  kilometres  (approx.). 

SQUARE  MEASURES* 
square  metre  =  10*7643  square  feet, 
square  foot  =  -0929  square  metre, 
acre  =  4046-71  square  metres, 
feddan  =  4200-83  square  metres, 
feddan  =  1-038  acres, 
hectare  =  10,000  square  metrsa, 
hectare  =  2*4711  acres, 
square  mile  =  640  acres, 
square  mile  =  27,878,400  square  feet, 
square  kilometre  =  100  hectares, 
square  kilometre  =  247  acres. 

CUBIC  MEASURES. 

cubic  foot  =  6*2355  gallons. 

cubic  foot  =  28-3  litres. 

cubic  foot  =  -028315  cubic  metre. 

cubic  metre  =  35-3166  cubic  feet. 

cubic  metre  =  61,028  cubic  inchea 

litre  =  61-02  cubic  inches. 

litre  =  '0353  cubic  feet. 


268  APPENDIX. 

i  litre  =  "2,1  gallon. 

i  litre  =  -88  quart. 

i  litre  =  176  pint. 

i  cubic  metre  =  220-097  gallons. 

i  gallon  =  '004543  cubic  metre. 

i  acre  foot  =  43,560  cubic  feet. 

i  acre  foot  =  1233*4  cubic  metres. 

1,000,000  cubic  feet  =  23  acre  feet  (approx.). 

DISCHARGE  MEASURES. 

i  cubic  foot  a  second  is  sometimes  abbreviated  to 

i  cusec  in  India,  and  to 

i  second  foot  in  America. 

i  second  foot  =  50  California,  Nevada,  Idaho,  or  Utah  inches 

i  second  foot  =  38*4  Colorado  inches. 

i  cubic  foot  a  second  amounts  to  86,400  cubic  feet  a  day,  or  2,445  cubic 

metres  a  day. 
1,000,000  cubic  metres  a  day  is  given  by  a  discharge  of  11-5741  cubic 

metres  a  second,  or  409  cubic  feet  a  second, 
i  cubic  foot  a  second  for  30  days  gives  59^  acre  feet, 
i  cubic  foot  a  second  for  24  hours  gives  2  acre  feet  (approx.). 
100  California  inches  for  24  hours  gives  4  acre  feet. 
100  Colorado  inches  for  24  hours  gives  5^  acre  feet, 
i  acre  foot  is  given  by  25*2  California  inches  in  24  hours. 

DUTY  OF  WATER. 

Equivalent  Expressions. 

i  cubic  foot  a  second  per  100  acres  gives  the  same  allowance  as 

i  cubic  metre  a  second  per  1430  hectares,  or  i  cubic  metre  a  second  per 

3402  feddans,  or  25-4  cubic  metres  a  day  for  each  feddan. 
i  litre  per  second  per  hectare  gives  the  same  allowance  oi  water  as 

i  cubic  foot  per  second  per  70  acres. 


APPENDIX    II, 


FORMULAS  AND   DISCHARGE   MEASUREMENTS. 

THE  formulas  in  most  common  use  by  irrigation  engineers  are  those 
which  relate  to  the  flow  of  water  in  open  cnanueis ,  to  discharges  over 
weirs,  both  clear  overfall  and  submerged  ;  and  to  discharges  through  the 
vents  of  canal  or  river  regulators,  lock  sluices  and  syphon  barrels. 

Tne  fundamental  formulas  on  which  the  whole  science  of  hydraulics  is 
based  are  three,  namely  : — 

Formula  (i).    Q  =  A  X  V. 

Formula  (2).    V  =  c  V  i  g  H. 

Formula  (3).     V  =  c  A/~RST 

The  symbols  contained  in  these  formulas  have  the  following 
significations : — 

A  is  the  area  of  any  section  of  discharging  waterway. 

V  is  the  mean  velocity  of  that  section. 

Q  is  the  discharge. 

g  is  gravity  acceleration. 

H  is  the  head  of  water. 

c  is  a  co-efficient  (given  in  Tables)  depending  on  the  nature  and 
condition  of  the  discharging  waterway. 

R  is  the  hydraulic  mean  depth  or  mean  radius ;  its  value  is  obtained  by 
dividing  the  area  of  the  water  cross  section  by  its  wetted  perimeter. 

S  is  the  hydraulic  slope  or  sine  of  the  inclination  of  the  water  surface, 
or,  in  other  words,  the  fall  of  water  surface  per  unit  of  length  of 
channel. 

Formula  (i)  is  applicable  in  all  cases  ;  Formula  (3)  is  applicable  to  open 
channels ;  Formula  (2)  to  sluice  ways. 

The  formulas  for  weir  discharges  are  deduced  from  Formula  (2).  That 
for  a  clear  overfall  weir,  without  velocity  of  approach,  is 

Formula  (4).     Q  =  §  c  X  A  \/  2  gh 

in  which  h  is  the  depth  of  water  on  the  weir  sill.     In  this  case  A  =  the 
length  of  the  weir  crest  X  I. 


2/0 


APPENDIX. 


The  formula  for  a  submerged  weir,  without  velocity  of  approach,  is 

Formula  (5).    Q  =  c  X  I  V~z~l&{d*  +  §  ^}. 
in  which  /  is  the  length  of  the  weir  crest, 

d\  is  the  difference  of  level  between  the  water  surfaces  up  stream 

and  down  stream  of  the  weir, 

and  d%  is  the  depth  of  the  sill  crest  below  the  down-stream  water 
surface. 

If  there  is  velocity  of  approach,  as  is  usually  the  case  with  canal  falls, 
allowance  has  to  be  made  for  it.  The  head  of  water  which  would  produce 
the  known  velocity  of  approach  must  be  calculated  from  Formula  (2) — 
V  =  c  V  2  ^H — and  be  added  to  the  head  of  water  in  Formulas  (4)  and  (5). 
In  Formula  (4)  it  is  added  to  h,  in  Formula  (5)  to  d\. 

The  value  of  gravity  acceleration  g  varies  in  different  parts  of  the  world, 
from  32*25  to  32*09  feet  per  second  :  but  it  is  usually  taken  as  32*2  feet  per 
second ;  and  that  is  the  figure  to  substitute  for  g  in  the  formulas  when 
English  measures  are  used.  But  if  metric  measures  are  used,  g  =  9-83, 
the  equivalent  for  32-2  feet  a  second.  Confusion  will  result,  when  using 
the  formulas  containing  g,  if  a  change  is  made  from  one  system  of  measures 
to  another  and  this  alteration  of  the  numerical  value  of  g  is  forgotten. 

The  value  of  the  co-efficient  c  is  given  in  Tables  for  different  values 
of  R,  the  hydraulic  mean  depth.  But  here  again,  the  value  of  c  changes 
with  change  of  measures  employed,  and  separate  Tables  of  Values  for  c 
are  required  for  R  in  feet  and  R  in  metres.  Bazin's  Values  have,  perhaps, 
been  more  generally  accepted  than  others  by  hydraulic  engineers,  and  are, 
therefore,  here  given — Table  I.  for  use  with  English  measures,  and 
Table  II.  for  use  with  metric  measures  : — 

TABLE  I. 

BAZIN'S    VALUES   OF  c  IN  THE  FORMULA  V  =  c  ^/RS  FOR  USE  WITH 
ENGLISH  MEASURES. 


Hydraulic  Mean 
Depth. 
R  in  Feet. 

Material  of  Bed  and  Sides  of  Channel. 

Plastered. 
Planed  Planks. 

Dressed  Stone. 
Brickwork. 

Rubble  Masonry. 

Earth. 

•25 

I25-4 

94-8 

56-5 

25-9 

'50 

I35-3 

108-8 

72-0 

35'7 

'75 

139-1 

115*0 

80-8 

42-6 

I'OO 

141*2 

118-5 

86-7 

47-9 

1-25 

142-4 

120-8 

90-9 

52-3 

1-50 

I43'3 

122*4 

94-0 

56*0 

i'75 

I43-9 

I23'6 

96-5 

59-2 

2'OO 

144-4 

I24'5 

985 

62*0 

3-50 

I45-I 

I25-8 

101-5 

66-6 

3'00 

I45'6 

126*7 

103-6 

70-4 

3-50 

I45-9 

I27-3 

105-2 

73*5 

4'00 

146'  I 

I27-8 

106-5 

76-1 

5-oo 

I46'5 

I28-5 

108-2 

80-2 

6-00 

147 

129 

no 

83-4 

APPENDIX. 


271 


TABLE   I.— continued. 


Hydraulic  Mean 
Depth. 
R  in  Feet. 

Material  of  Bed  and  Sides  of  Channel. 

Plastered. 
Planed  Planks. 

Dressed  Stone. 
Brickwork. 

Rubble  Masonry. 

Earth. 

7  '00 

147 

I2Q 

1  10 

86-0 

8-00 

147 

130 

III 

88-0 

lO'OO 

J47 

130 

112 

91-2 

I2'00 

147 

130 

H3 

93'4 

15-00 

147 

130 

114 

95'9 

20-00 

148 

131 

U5 

98-6 

40*00 

148 

131 

116 

103-1 

yo'oo 

148 

131 

116 

105-2 

lOO'OO 

148 

131 

116 

106-1 

Inf. 

148 

131 

117 

108-3 

TABLE   II. 

BAZIN'S  VALUES   OF  c  IN  THE    FORMULA  V  =  c 
METRIC  MEASURES. 


KS  FOR   USE  WITH 


Hydraulic  Mean 
Depth. 
R  in  Metres. 

Material  of  Bed  and  Sides  of  Channel. 

Plastered. 
Planed  Planks. 

Dressed  Stone. 
Brickwork. 

Rubble  Masonry. 

Earth. 

0-05 

65 

47 

26 

___ 

O'lO 

72 

56 

35 

16 

0-15 

73 

60 

40 

20 

O'20 

76 

62 

43 

22 

0-25 

77 

64 

46 

24 

0-30 

78 

65 

48 

26 

0'35 

78 

66 

49 

28 

0'40 

79 

67 

5i 

29 

0-50 

79 

68 

53 

32 

0'60 

80 

69 

54 

34 

O'7O 

80 

69 

55 

36 

0'80 

80 

70 

56 

37 

I'OO 

80 

70 

58 

40 

1-50 

81 

7i 

60 

44 

2'00 

81 

71 

61 

47 

2-50 

81 

72 

61 

49 

3-00 

81 

72 

62 

50 

4"OO 

81 

72 

63 

52 

5-00 

81 

72 

63 

54 

lO'OO 

81 

72 

64 

56 

15-00 

81 

72 

64 

57 

The  above  Tables  of  values  for  c  takes  into  account  the  roughness  of  the 
bed  and  the  hydraulic  mean  depth,  but  not  the  hydraulic  slope,  which  in 
extreme  cases  has  to  be  considered.  In  all  ordinary  canals  and  rivers  the 


272  APPENDIX. 

value  of  c  is  not  affected  by  the  slope.  But  in  mountain  torrents  and  in 
channels  with  a  very  gentle  surface  slope,  such  as  the  tail  reaches  of  rivers 
near  the  sea,  the  hydraulic  slope  is  a  factor  to  be  taken  into  account  for 
determining  the  correct  value  of  c.  The  formula,  known  as  Ganguillet 
and  Kutter's,  embraces  this  consideration,  the  value  of  c  in  the  formula, 
V  =  c  V  R  S,  being  represented  by  the  expression 


in  which  n  is  the  coefficient  of  roughness  depending  on  the  nature  of  the 
surface  of  the  channel,  and  a,  I  and  m  are  constants  derived  from 
experiment,  the  other  letters  having  the  same  signification  as  in 
Formula  (3)  above. 

When  the  values  of  the  symbols  in  the  formula  are  expressed  in  English 
feet,  a,  lt  and  m  have  the  following  values : — 

a  =  41 '6604676. 

/   =  1-8113250. 

m  —  0-0028075. 
When  metrical  measures  are  used, 

a  =  23. 

I  =  i. 

m  =  -00155. 

n  has  the  following  values  for  channels  of  different  surfaces  :— 


Values  of  n. 


It  =  -010 


n  =  -013 
n  =  -017 

n  —  -025 


n  =  -035 


Nature  and  Material  of  Channel. 


Plaster  in  pure  cement :  planed  timber  :  glazed,  coated 
or  enamelled  stoneware  and  iron  pipes :  glazed  surfaces  of 
every  sort  in  perfect  order. 

Ashlar  and  well-laid  brickwork. 

Brickwork,  ashlar  and  stoneware  in  an  inferior  con 
dition :  rubble  in  cement  or  plaster,  in  good  order. 

Canals  and  rivers  in  earth  of  tolerably  uniform  cross- 
section,  inclination  and  direction,  in  moderately  good  order 
and  regimen,  and  free  from  stones  and  weeds. 

Rivers  and  canals  with  earthen  beds  in  bad  order  and 
regimen,  and  having  stones  and  weeds  in  great  quantities. 


Experience  is  required  for  the  assignment  of  the  correct  value  to  «.  Its 
usual  value  for  the  earthen  channels  of  an  ordinary  canal  system  in  normal 
condition  would  be  -025. 

The  calculation  of  discharges  from  hydraulic  formulas  is  much  facilitated 
by  the  use  of  Tables  made  for  that  purpose.  In  India,  where  discharges 
are  measured  in  feet, Higham's  "Hydraulic  Tables"  and  Jackson's  "Canal 
and  Culvert  Tables  "  are  most  in  favour.  "  New  Tables  for  the  complete 


APPENDIX. 


273 


solution  of  Ganguillet  and  Kutter's  Formula  for  the  flow  of  liquid  in  Open 
Channels,  Pipes,  Sewers  and  Conduits,"  by  Colonel  E.  C.  S.  Moore,  R.E., 
M.S.I.,  will  also  be  found  useful  by  calculators  who  work  with  English 
measures.  In  Egypt,  where  the  metrical  system  is  current,  "  Elementary 
Hydraulics,"  by  Willcocks  and  Holt,  is  a  safe  and  simple  guide  to  the 
practical  use  of  hydraulic  formulas.  "  The  Civil  Engineer's  Pocket  Book," 
by  Trautwine,  shows  how  the  formulas  should  be  used  in  both  cases,  that 
is,  with  English  and  metric  measures.  But  it  is,  perhaps,  advisable,  in 
dealing  with  formulas  which,  to  many,  may  be  sufficiently  intricate  without 
unnecessary  complication,  to  make  use  of  a  book  of  reference  on  the  sub- 
ject which  deals  exclusively  either  with  formulas  and  coefficient  values 
adapted  to  English  measures,  or  with  those  adapted  to  metric  measures ; 
and  not  to  one  which,  like  this  Appendix,  attempts  to  deal  with  both. 
However,  as  this  book  may,  on  occasion,  possibly  be  available  when  others 
are  not,  the  two  following  Tables  are  given,  from  which  the  values  of  c  in 
Kutter's  formula  may  be  obtained  for  the  usual  value  of  n — viz.,  '025 — 
applicable  to  the  ordinary  channels  of  a  canal  system. 

TABLE    III. 

(For  use  with  English  Measures.) 
KUTTER'S   VALUES  OF  c  IN  THE  FORMULA  V  =  c  */  K  S  FOR    ORDINARY 

CHANNELS  IN  NORMAL  CONDITION,  WHEN  «  —  '025. 


Hydraulic 
Mean 
Depth  R 
in  feet. 

S 

I 
40,000 

S 
i 
20,000 

S 

I 

10,000 

S 
I 

5,000 

S 

i 
2,500 

S 

i 

1,000 

S 

I 
"100 

•10 

J7 

20 

22 

24 

25 

27 

27 

'20 

24 

26 

29 

31 

32 

34 

34 

•40 

32 

35 

38 

40 

42 

43 

44 

•60 

38 

4i 

44 

46 

47 

48 

49 

•80 

43 

46 

48 

50 

5i 

52 

53 

roo 

47 

49 

52 

54 

55 

56 

56 

1-50 

55 

57 

59 

60 

61 

62 

62 

2*00 

61 

62 

64 

64 

65 

66 

66 

3'00 

70 

7i 

7i 

7i 

7i 

7i 

71 

3*28 

72 

72 

72 

72 

72 

72 

72 

4'00 

78 

77 

76 

76 

76 

75 

76 

6-oo 

88 

85 

84 

82 

81 

81 

81 

8-00 

96 

9i 

88 

87 

85 

84 

83 

lO'OO 

1  02 

96 

92 

89 

88 

87 

86 

I2'00 

107 

99 

94 

92 

90 

88 

87 

1  6-00 

U5 

106 

99 

94 

93 

9i 

90 

20'OO 

121 

no 

102 

98 

96 

94 

93 

30-00 

133 

118 

108 

103 

99 

96 

95 

50-00 

147 

127 

114 

108 

104 

101 

100 

75*00  j   157 

133 

118 

in 

106 

103 

1  02 

lOO'OO 

163       137 

121 

"3 

108 

105 

104 

274 


APPENDIX. 


TABLE    IV. 

(Fov  use  with  Metric  Measures.} 
KUTTER'S  VALUES  OF  c  IN  THE  FORMULA  V  =  c  V  R  S  FOR  ORDINARY 

CHANNELS    IN    NORMAL    CONDITION,    WHEN    tt  =  '025. 


Hydraulic 

S 

S 

S 

s 

s 

s 

s 

Mean 

Depth  R 

I 

I 

i 

i 

i 

i 

i 

in  metres. 

40,000 

20,000 

10,000 

5,ooo 

2,500 

1,000 

IOO 

•025 

9 

10 

II 

12 

13 

13 

14 

"05 

12 

13 

15 

16 

17 

18 

18 

•10 

*7 

18 

19 

20 

21 

22 

22 

*20 

22 

23 

24 

25 

26 

27 

27 

•30 

26 

28 

29 

30 

30 

31 

31 

"SO 

31 

32 

33 

34 

34 

35 

35 

I  '00 

40 

40 

40 

40 

40 

40 

40 

2*OO 

50 

48 

47 

46 

45 

45 

45 

3'00 

56 

53 

5i 

49 

48 

48 

47 

5*00 

64 

59 

54 

53 

52 

5i 

50 

lO'OO 

75 

66 

60 

57 

55 

54 

53 

15-00 

81 

7i 

63 

59 

57 

56 

55 

20'00 

85 

72 

64 

60 

58 

57 

56 

30-00 

90 

76 

67 

62 

60 

58 

57 

The  formulas  (2),  (4)  and  (5),  for  calculating  the  discharges  of  sluices, 
weirs  and  syphons,  apply  to  any  system  of  measures,  to  the  metric  as  well 
as  to  the  English.  But  it  is  necessary  that  the  head,  the  length  or  area, 
and  the  acceleration  of  gravity  (g)  should  all  be  in  the  same  unit — either  all 
in  feet,  or  all  in  metres,  or  all  in  any  other  unit  of  measurement.  The 
discharges  will  also  be  in  the  cube  of  that  unit.  The  value  of  g,  as  has 
been  stated  already,  is  32*2  feet  in  English  measure,  and  9-83  metres  in 
metric.  The  values  of  c  given  in  the  following  table  are  the  same  what- 
ever system  of  measures  may  be  used ;  since  c  in  each  of  the  formulas  (2), 

(4)  and  (5)    =      actual  discharge       a  relation  which  is  independent  of 

theoretical  discharge 
systems  of  measures. 

TABLE    V. 
VALUES    OF    c    GENERALLY    EMPLOYED    IN    PRACTICE    WITH    DISCHARGE 

FORMULAS    OF    SLUICES,    WEIRS    AND    SYPHONS.          FORMULAS     (2),    (4) 
AND    (5). 


Description  of  Discharge  Waterway. 


Coefficient  c. 


Ordinary  lock  sluices  and  small  sluices     ... 

•Clear  overfall  weirs 

Small  regulator  openings  with  shallow  water 


•62 
•62 
'57 


APPENDIX.  275 

TABLE  V.— continued. 


Description  of  Discharge  Waterway.  I     Coefficient  c. 


Regulator  openings,  under  6  feet  or  2  metres  in  width, 
with  recesses  in  the  piers 


Ditto,  ditto,  with  straight  continuous  piers  

Regulator  openings  between  6  and  13  feet  (2  and  4  metres) 


in  width,  with  recesses  in  the  piers 


Ditto,  ditto,  with  straight  continuous  piers  

Regulator  openings  over  13  feet  (4  metres)  in   width, 


with  recesses  in  the  piers 

Ditto,  ditto,  with  straight  continuous  piers 

Short  straight  pipes  as  in  syphons 

Short  bent  pipes  as  in  syphons        ...         „ 


•62 

72 

•72 
•82 

•82 
•92 

•82 
72 


Formula  (3),  V  =  c  i/  R  S,  for  open  channels  is  of  more  practical 
use  in  the  preparation  of  a  project — to  determine,  for  example,  the  dimen- 
sions of  a  canal  or  the  possible  maximum  discharge  of  an  existing  natural 
waterway — than  it  is  to  ascertain  the  actual  discharges  of  flowing  canals. 
The  more  usual  way  of  gauging  actual  discharges  is  to  ascertain  the  mean 
velocity  by  direct  observations  made  with  floats.  The  mean  velocity 
itself  may  be  observed  by  special  floats  in  the  form  of  rods  weighted  so  as 
to  maintain  a  vertical  position,  and  of  such  lengths  that  they  float  with 
their  lower  ends  just  clear  of  the  bed.  The  rate  of  travel  of  these  rods 
should  be  observed  along  lines  in  the  direction  of  the  flow  and  equidistant 
from  one  another  across  the  channel.  The  mean  of  all  the  observed 
velocities  will  give  the  mean  velocity. 

But  the  more  ordinary  method  employed  is  to  observe  the  maximum 
surface  velocity,  and  from  it  to  calculate  the  mean  velocity.  All  the 
apparatus  required  is  a  watch,  an  empty  bottle  or  other  simple  float,  and 
means  of  measuring  the  cross  sections  of  the  channel  and  intervening 
length  which  will  be  used  as  the  "  run  "  for  timing  the  rate  of  travel  of  the 
float.  The  mean  velocity  will  then  be  obtained  from  the  observed  maxi- 
mum surface  velocity  by  the  use  of  the  following  formula,  in  which  V  is  the 
mean  velocity,  U  is  the  maximum  surface  velocity,  and  c  is  a  coefficient 
having  the  same  values  as  in  formula  (3),  V  =  c  A/  R  S,  as  given  in  Tables 
I.  and  II.  for  English  and  metric  measures  respectively.  These  formulas 
which  follow  apply  only  to  ordinary  canals,  drains  and  water-courses  on 
straight  reaches  of  uniform  section. 

Formula  (6  A).  V  =  U  X  g  .  c  for  English  measures  (c  values  of 
Table  I.). 

Formula  (6  B).      V  =  U  X   — j—  for  metric  measures  (c  values    of 

Table  II.). 

It  will  be  found  that,  if  there  are  substituted,  in  the  upper  and  lower 

T  2 


276 


APPENDIX. 


equations  respectively,  values  of  c  from  Tables  I.  and  II.  for  corresponding 
values  of  R— as,  for  instance,  for  R  ~  3-28  feet,  Table  I.,  and  R  =  i  metre, 
Table  II. — the  two  expressions  will  give  the  same  numerical  result.  The 
Formula  (6  C),  V  =  Ci  U,  can,  therefore,  be  substituted  for  either,  and  the 
values  of  c  be  tabulated.  This  has  been  done  and  the  following  table  is 
the  result. 

TABLE    VI. 
VALUES  OF   c,    IN    THE    FORMULA  V  =  ct  U    FOR   FINDING    MEAN    FROM 

SURFACE    MAXIMUM    VELOCITY. 


Hydraulic 
Mean  Depth  R 
in  feet. 

Material  of  bed  and  sides  of  Channel. 

Hv.lr.ml'C 
Mcali  D..pth  R 
in  metres. 

Plastered. 
Planed  Planks. 

Dressed  Stone. 
Brickwork. 

Rubble 
Masonry. 

Earth. 

I'OO 

•85 

•83 

77 

•65 

•30 

2*00 

•85 

'S3 

*79 

•71 

•60 

3'00 

•85 

•83 

•80 

'73 

•QO 

3-28 

•85 

•83 

•80 

'74 

I  'CO 

4*00 

•85 

•83 

•81 

'75 

I  '20 

5*oo 

•85 

•83 

•81 

•76 

I-50 

6*00 

•85 

'84 

•81 

'77 

j-8o 

6-50 

•85 

•84 

•81 

'77 

2*00 

8-00 

'85 

•84 

•82 

•78 

2'50 

lO'OO 

•85 

'84 

•82 

•78 

3-00 

I2'OO 

•85 

•84 

•82 

'79 

3'5o 

18-00 

•85 

'84 

•82 

'79 

5'5o 

2O'OO 

•85 

•84 

•82 

•80 

6-00 

70-00 

•85 

•84 

•82 

•8i 

31*00 

Inf. 

•85 

•84 

•82 

•81 

Inf. 

Formulas  (6  A)  and  (6  B),  and  their  substitute  Formula  (6  C),  apply  to 
all  canals  on  reaches  where  the  maximum  surface  velocity  keeps  steadily 
to  midstream,  provided  the  reach  itself  is  fairly  straight  and  uniform. 

Willcocks  and  Holt  in  "  Elementary  Hydraulics,"  written  for  the  use  of 
engineer  students,  give  the  following  simple  directions  as  to  the  ordinary 
method  in  which  a  discharge  observation  should  be  made. 

"  Select  a  fairly  straight  reach  of  about  3  kilometres  in  length,  put  in  a 
flag  on  one  bank  at  about  the  middle  point,  taking  care  that  the  central 
velocity  is  the  maximum.  Measure  25  metres  upstream  and  25  metres 
downstream,  and  put  up  two  more  flags,  and  three  flags  exactly  opposite 
these  on  the  other  bank.  Take  three  cross  sections  of  the  canal  at  these 
three  places.  Take  the  mean  of  the  two  outer  sections,  and  then  take  the 
mean  of  this  mean  and  the  middle  section.  This  last  mean  is  the  actual 
cross  section  of  the  canal.  Now  allow  some  twenty  circular  discs  of  wood 
of  about  10  centimetres  diameter  and  2  centimetres  thickness  to  pass  down 
the  centre  of  the  canal,  and  record  the  number  of  seconds  they  each  take 
to  pass  the  interval  between  the  outer  flags.  The  mean  of  these  twenty 


APFLJND1X.  277 

observations  divided  into  50  metres  gives  the  maximum  surface  velocity  in 
metres  per  second.  Find  A  (area)  and  R  (hydraulic  mean  depth)  from  the 
cross  section  in  metres  ;  we  have  U  ;  and  CL  can  be  obtained  from  Table 
VI.  by  noting  carefully  the  actual  condition  of  the  canal.  Then  V  =  c^  x  U 
in  metres  per  second,  and  Q  —  A  X  V  in  cubic  metres  per  second.  Of 
course  discharge  by  surface  velocity  observations  can  only  be  taken  when 
there  is  no  wind." 

If  the  discharge  of  a  wide  river  with  an  irregular  bed  has  to  be  measured, 
a  more  elaborate  method  must  be  adopted.  A  cross  section  of  the  river 
must  be  made  with  the  aid  of  a  steamer  to  take  soundings  and  of  a  theodo- 
lite to  fix  the  position  of  the  steamer  at  the  moment  of  taking  the  soundings. 
Ranging  rods,  fixed  on  the  bank  in  prolongation  of  the  line  of  the  cross 
section,  will  enable  the  steamer  to  take  up  its  position  for  sounding  on  the 
right  alignment.  On  account  of  the  uneven  section  the  surface  velocities 
must  be  observed  at  numerous  points,  and  the  calculation  of  the  discharge 
be  made  separately  for  each  portion  of  the  cross  section  to  which  the 
observed  velocities  belong.  The  total  discharge  of  the  river  will  then  be 
the  sum  of  the  discharges  of  the  subdivisions  which  have  been  separately 
calculated.  _ 

The  formula  for  open  channels,  V-=c  \/  R  S,  as  developed  in  Kuttei1? 
formula,  can  be  applied  to  pipe  discharges  by  giving  a  suitable  value  to 
n.  For  iron  pipes  in  good  order,  and  from  i  inch  to  4  feet  diameter,  «  may 
be  taken  at  from  'oio  to  '012  according  to  the  condition  of  the  inner  sur- 
face of  the  pipe,  the  lower  figures  being  used  if  the  pipe  is  in  exceptionally 
good  condition,  and  the  higher  figures  when  the  condition  is  not  so  good, 
though  still  good. 

There  are  thus  six  formulas  which  are  most  essential  for  irrigation 
engineers,  namely  : 

Formula  (i).     Discharge  Q  =  A  x  V  for  all  cases. 

Formula  (2).     Mean  velocity  V  =  c  V  2~gK  for  sluice-ways. 

Formula  (3).     Mean  velocity  V  =  c  \/  R  S  foi  open  channels  and  pipes. 

Formula  (4).    Discharge  Q  =  §  c  A  \  i  g  h  for  clear-  overfall  weirs. 

Formula  (5).  Discharge  Q  =  c  X  I  V  2  g  di  (d%  +  f  <y  for  submerged 
weirs. 

Formula  (6  A).     Mean  velocity  V=U  X  -^-37   for  English  measures 


or  Formula  (6  B),  mean  velocity  V=U  X    T     ,   c   for    metric    measures, 

or  Formula  (6  C),  mean  velocity  V  =  Cj  U,  in  place  of  Formulas  (6  A) 
and  (6  B). 


APPENDIX    III. 


BOOKS  OF  REFERENCE. 

IN  the  following  list  those  works  of  reference  only  are  included  which 
deal  with  irrigation,  or  one  of  its  main  sub-heads,  in  a  general  way. 
Books,  reports,  proceedings,  and  pamphlets,  which  treat  of  special 
irrigation  schemes  or  constructions,  are  too  numerous  for  accommodation 
in  an  appendix.  Catalogues  of  such  works  exist  in  technical  libraries. 

IRRIGATION,  GENERAL. 

"  Irrigation."  Transactions  of  the  American  Society  of  Civil  Engineers. 
International  Congress.  1904. 

A  collection  of  papers  on  irrigation  (i)  under  British  engineers,  that  is,  in 
India  and  Egypt ;  (2)  in  Java ;  (3)  in  the  United  States ;  (4)  in  France  ;  and 
(5)  in  the  Hawaiian  islands,  with  discussions  on  the  papers. 

"Irrigation  Engineering,"  by  H.  M.  Wilson.  Publishers:  Chapman 
&  Hall,  London,  and  Wiley  &  Sons,  New  York.  1903. 

The  subject  is  viewed  from  an  American  standpoint.  Most  of  the  illustrations 
are  borrowed  from  the  United  States,  but  some  are  drawn  from  India  and  other 
countries.  A  list  of  books  of  reference  (chiefly  American)  is  given  for  each 
section  of  the  subject. 

"  Manual  on  Irrigation  Works,"  by  B.  O.  Reynolds.  Printed  Govern- 
ment Press,  Madras.  1906. 

This  book  is  written  with  India  as  the  author's  standpoint,  and  is  a  text-book 
for  the  use  of  the  students  of  the  Madras  Engineering  College,  compiled  by  one 
of  the  staff. 

"  Irrigation  Manual,"  by  Lieut.-Gen.  J.  Mullins.  Publishers  :E.  and  F.  N. 
Spon,  London  and  New  York.  1890. 

This  is  also  written  from  an  Indian  standpoint.  It  contains  many  plates  of 
irrigation  works  existing  in  1890. 

"  Irrigation  Canals  and  other  Irrigation  Works,"  by  P.  J.  Flynn. 
Published  San  Francisco,  California.  1892. 

The  subject  is  treated  generally,  with  illustrations  borrowed  from  America, 
India  and  other  countries. 

"  Hydraulic  Works,"  by  Lowis  D'A.  Jackson.  Publishers :  Fhacker  &  Co., 
London.  1885. 

Statistics  are  given  of  the  hydraulic  works  and  hydrology  of  England, 
Canada,  Egypt  and  India. 

'  Irrigation  Pocket  Book,"  by  R.  B.  Buckley.  Publishers :  E.  &  F.  N. 
Spon  Ltd.,  London;  Spon  and  Chamberlain,  New  York;  Thacker  & 
Co.,  India.  1911. 

A  comprehensive  compilation  of  facts,  figures,  and  formulae  bearing  on  the  everyday 
work  of  an  Irrigation  Engineer. 


APPENDIX.  279 

IRRIGATION  IN  DIFFERENT  COUNTRIES. 
India. 

"  The  Irrigation  Works  of  India,"  by  R.  B.  Buckley.  Publishers  :  E.  and 
F.  N.  Spon,  London  and  New  York.  1905. 

This  is  the  most  complete  and  recent  work  which  treats  of  irrigation  in  India 
as  a  whole.  The  magnificent  irrigation  works  are  described  and  freely  illus- 
trated ;  and  the  lessons  taught  by  experience,  gained  in  irrigation  schemes  of 
large  scale  and  extending  over  long  periods,  are  recorded.  Almost  all  matters 
connected  with  practical  irrigation  are  dealt  with. 

"Irrigated  India,"  by  Hon.  A.  Deakin.  Publishers:  Thacker  &  Co., 
London.  1893. 

This  book  contains  a  description  of  the  irrigation  and  agriculture  of  India 
and  Ceylon  as  viewed  by  an  Australian. 

"  Irrigation  in  India,"  by  H.  M.  Wilson.  Printed  Government 
Printing  Office,  Washington.  1892. 

The  subject  is  presented  as  viewed  by  an  American  engineer. 

"  Report  of  the  Indian  Irrigation  Commission,"  presided  over  by 
Sir  Colin  Scott-Moncrieff.  Publishers :  Eyre  &  Spottiswoode.  1903. 

This  report  contains  a  record  of  the  evidence  collected  by  the  Commission 
concerning  the  facts  about  Indian  irrigation,  and  its  recommendations  as  to  the 
policy  that  the  Indian  Government  should  adopt  with  reference  to  future 
irrigation  schemes. 

Egypt- 

"Egyptian  Irrigation,"  by  Sir  W.  Willcocks  and  J.  I.  Craig.  Pub- 
lishers: E.  &  F.  N.  Spon,  London  and  New  York.  1913. 

This  is  the  standard  work  on  irrigation  in  Egypt.  It  contains  an  account  of 
its  canal  systems,  and  records  the  experience  of  the  irrigation  staff  gained 
since  1883  and  the  opinions  formed  as  a  result  of  that  experience. 

America. 

"Irrigation  in  the  United  States,"  by  F.  H.  Newell.  Publishers: 
Crowell  &  Co.,  New  York. 

This  book  is  intended  for  the  edification  of  pioneer  settlers  in  a  new  country, 
and  therefore  is  not  technical.  It  treats  of  constructions  and  methods  more  or 
less  primitive. 

"  Irrigation  in  Western  America,"  by  Hon.  A.  Deakin.  Printed 
Government  Press,  Melbourne.  1885. 

The  author  gives  an  Australian's  view  of  the  subject. 

"  Irrigation  in  Southern  California,"  by  W.  Ham  Hall.  Published 
State  Office,  Sacramento.  1888. 

The  irrigable  regions  and  the  works  and  projects  of  Southern  California 
a-e  described. 

Europe. 

"Italian  Irrigation,"  by  Captain  R.  Baird  Smith,  R.E,  Publishers: 
Smith,  Elder  &  Co.,  London.  1855, 


280  APPENDIX. 

"Irrigation  du  Midi  de  1'Espagne,"  by  Maurice  Aymard  Publisher: 
Eugene  Lacroix,  Paris.  1864. 

"  Irrigation  in  Southern  Europe,"  by  Lieut.  C.  C.  Scott- Moncrieff,  R.E. 
Publishers:  E.  and  F.  N.  Spon,  London.  1868. 

The  three  foregoing  works  give  general  descriptions  of  the  practice  of 
irrigation  in  the  southern  countries  of  Europe.  They  are  not,  however,  intended 
to  be  books  of  reference  for  engineers  intent  upon  the  more  purely  technical 
studies  of  their  profession. 

RIVERS  AND  NAVIGATION. 

"The  Improvement  of  Rivers,"  by  B.  F.  Thomas  and  D.  A.  Watt. 
Publishers :  Chapman  &  Hall,  London;  Wiley  &  Sons,  New  York. 

This  book  treats  of  dredging,  training  works,  spurs,  bank  protection,  flood 
banks,  storage  reservoirs  for  navigation,  locks,  lock  gates  and  valves,  fixed 
dams  (weirs),  movable  dams  and  regulating  apparatus. 

"  Rivers  and  Canals,"  by  L.  F.  Vernon-Harcourt.  Published  Clarendon 
Press,  Oxford.  1896. 

This  book  deals  with  the  flow,  control  and  improvement  of  rivers,  and  the 
design,  construction  and  development  of  canals,  both  for  navigation  and  irrigation, 
and  gives  statistics  of  the  traffic  on  inland  waterways. 

DAMS  AND  RESERVOIRS. 

"  Design  and  Construction  of  Masonry  Dams,"  by  Edward  Wegmann. 
Publishers:  Chapman  &  Hall,  London;  Wiley  &  Sons,  New  York.  1911. 

This  work  gives  diagrams  and  descriptions  of  the  existing  high  dams  studied  as 
a  preliminary  to  the  designing  of  the  Quaker  Bridge  dam  and  its  substitute,  the 
New  Croton  dam. 

"  Reservoirs  for  Irrigation,"  by  James  D.  Schuyler.  Publishers : 
Chapman  &  Hall,  London;  Wiley  &  Sons,  New  York.  1901. 

Descriptions  are  given  of  the  various  types  of  dams,  and  the  book  is  profusely 
illustrated.  Information  is  also  given  about  the  natural  and  projected  reservoirs 
in  the  United  States  of  America. 

"  Masonry  Dams  from  Inception  to  Completion,"  by  C.  F.  Courtney. 
Published  1897. 

This  small  book  describes  shortly  the  method  of  designing  and  constructing 
dams. 

"  Indian  Storage  Reservoirs  with  Earthen  Dams,"  by  W.  L.  Strange. 
Publishers:  E.  and  F.  N.  Spon,  London  and  New  York. 

This  work  treats  fully  of  the  design  and  construction  of  earthen  dams,  and  of 
the  storage  problems  connected  with  them,  based  on  the  practice  of  the  engineers 
of  India  in  the  Bombay  Presidency. 

DRAINAGE  AND  RECLAMATION. 

"The  Drainage  of  Fens  and  Low  Lands,"  by  W.  H.  Wheeler. 
Publishers :  E.  and  F.  N.  Spon,  London.  1888. 

This  book  gives  a  general  description  of  works  and  machines  used  in  draining 
low  lands. 


APPENDIX.  28l 


CONSTRUCTION. 

"  Design  of  Irrigation  Works,"  by  William  Bligh.  Publishers :  Archibald 
Constable  &  Co.,  London. 

This  book  deals  with  the  theory  of  design  and  its  practical  application  to 
Irrigation  Works,  with  full  illustrations  ;  design  of  existing  works  are  critically 
examined. 

LfAA* 

"  Irrigation  Development,"  by  W.  Ham  Hall.  Published  State  Office, 
Sacramento.  1886. 

A  detailed  study  of  irrigation  legislation  in  France,  Italy  and  Spain  is  made 
with  the  view  of  framing  irrigation  laws  adapted  to  American  conditions. 


APPENDIX   IV. 


NOTES,   1919. 

Note  i  to  page  7.     Results  of  irrigation  reform  in  Egypt. 

The  Report  of  the  Ministry  of  Public  Works,  Egypt,  for  1914-15, 
summarises  the  results  of  irrigation  administration  in  Egypt  in  the 
following  passage  : — 

"  The  area  cultivated  has  increased  by  forty- three  per  cent,  since 
1882,  and  crop  has  increased  by  sixty-two  per  cent.  .  .  .  During  the 
past  thirty  years  an  annual  average  of  30,000  acres  of  entirely  new  land 
have  been  added  to  the  taxable  soil  of  the  country  and  now  produce 
two  crops  a  year  ;  an  average  of  40,000  acres  a  year  have  been  con- 
verted from  the  one-crop  system  ol  basin  irrigation  ;  and,  whereas  the 
average  area  that  went  without  water  from  the  flood  each  year  was 
about  90,000  acres,  an  average  of  not  more  than  1,000  acres  or  so  suffer 
in  that  way  now." 

Note  2  to  page  8.     The  Lower  Chenab  Canal,  Punjab. 

The  following  is  a  quotation  from  the  Government  of  India's  Review 
of  "  Irrigation  in  India  for  the  Year  1916-17  "  : — 

"  The  Lower  Chenab  Canal  is  easily  the  most  productive  canal  in 
India.  It  irrigates  2^  million  acres,  and  in  the  year  under  review  pro- 
duced a  net  revenue  of  141  lakhs  of  rupees  on  a  capital  outlay  of  324 
lakhs,  a  return  of  43!  per  cent.  The  accumulated  surplus  revenues 
from  this  canal,  after  paying  interest  charges,  amount  to  no  less  than 
1,271  lakhs  of  rupees." 

Note  3  to  page  19.     Canal  off-takes  from  rivers. 

As  regards  the  siting  of  the  channel  which  forms  the  off-take  of  a 
canal  from  a  silt-laden  river,  it  has  been  suggested  that  the  alignment 
of  such  a  channel  should  not  make  an  acute  angle  with  the  direction  of 
the  current  below  the  point  of  off-take,  nor  even  a  right  angle,  but  an 
obtuse  angle  ;  or,  in  other  words,  an  acute  angle  with  the  direction  of 
the  current  above  the  point  of  off-take.  Sir  William  Willcocks,  in  his 
projects  for  the  irrigation  of  Mesopotamia  (publishers,  E.  &  F.  N. 
Spon,  1911),  has  deliberately  designed  canal  off-takes  in  this  way  with 
the  object  of  avoiding  silt  trouble.  For  instance,  the  Left  Euphrates 
Canal  is  shown  on  his  Plan  48  taking  off  the  Euphrates  above  the 
Feluja  Barrage  in  a  direction  at  first  opposite  to  that  of  the  flow  of  the 


APPENDIX.  283 

river  upstream  of  the  barrage,  the  head  reach  of  the  canal  curving  round 
till  the  proper  general  alignment  is  attained. 

Note  4  to  page  37.     Summer  crop  area  of  Egypt. 

It  appears  from  the  Report  of  the  Ministry  of  Public  Works,  Egypt, 
for  1914 — 1915,  that  it  is  now  reckoned  that  in  Egypt  50  per  cent,  of  the 
gross  area  of  perennially  irrigated  land  is  annually  put  under  summer 
crop.  This  is  evident  from  column  V.  of  the  statement  showing  the 
areas  and  water  requirements  of  "  the  Existing  Cultivation  and  Possible 
Further  Extension  in  Egypt." 

Note  5  to  page  50.     Water  requirements  of  Egypt. 

The  calculation  of  the  additional  water  required  in  Egypt,  given  in 
the  statement  referred  to  in  the  foregoing  note,  is  based  on  an  allowance 
of  28  cubic  metres  a  day  for  150  days  per  acre  of  summer  crops  other 
than  rice,  and  of  (28  x  3  =  )  84  cubic  metres  a  day  for  75  days  per  acre 
of  rice.  The  conclusion  reached  is  that  the  total  additional  water 
required  by  Egypt,  over  and  above  what  the  enlarged  Assuan  reservoir 
and  the  natural  discharge  of  the  river  supplies,  is  9,555  million  cubic 
metres.  The  same  Report  gives  the  content  of  the  Assuan  reservoir  as 
2,400  million  cubic  metres.  The  sum  of  these  two  figures — 12,000 
million  cubic  metres  nearly — should  be  used  when  comparing  this  1915 
estimate  with  that  of  ten  or  twelve  years  earlier — namely,  6,000  million 
cubic  metres  before  the  Assuan  reservoir  contribution  was  taken  into 
account.  The  later  estimate  of  requirements  is  thus  double  the  earlier 
one.  The  increase  is  due  to — 

(1)  The  assumption  that  50  per  cent.,  instead  of  40  per  cent.,  of  the 

gross  area  is  annually  under  summer  crop  ; 

(2)  The  substitution  of  150  days  for  100  days  as  the  period  during 

which  storage  water  is  required  ; 

(3)  The  assumption  that  the  present  available  supply  is  insufficient 

in  a  low  summer  to  allot  any  of  it  to  the  existing  rice  area  ;  and 

(4)  The  adoption  of  84  cubic  metres  a  day  per  acre  of  crop,  instead 

of  50,  as  the  proper  allowance  for  rice. 

The  estimate  made  with  these  data  gives  a  result  which  may  safely 
be  called  liberal. 

The  present  additional  requirements  may  be  met  (i)  by  storage  in 
the  proposed  White  Nile  reservoir  (see  the  note  following),  (2)  by 
arrangements  to  minimise  the  loss  due  to  evaporation  in  the  Sudd 
region,  and  (3)  by  storage  in  Lake  Albert. 

The  White  Nile  reservoir  is  credited  with  a  probable  effective  storage 
of  3,000  million  cubic  metres  in  normal  years.  The  official  estimate  of 
requirements  is  calculated  on  the  basis  of  a  low  level  year  such  as  1914. 
The  estimate  of  the  means  of  supply  should  be  on  the  same  basis.  The 
White  Nile  reservoir  must,  therefore,  be  credited  with  something  less 
than  3,000  millions,  say,  2,000  millions. 

The  prevention  of  loss  in  the  Sudd  region  was  assumed  on  page  56  to 


I  AIMM-NWX. 

be   equivalent    to   an    elleetive    storage    <>|'    1,700    million 

(about     I  \\  i  )  I  hit  ds    ol      ',00    milln  MI  s.       Mil,    II 


smimie 

;;amci|    by 

<  la  1  1  y  JM  i 

2.\')  day:-,   the  <|iia 

oiirlhinl    on    i!  .    |oinm-y    t 

million  cubic  metres.      Of  this  th 

for  immediate  use.    Tin-  wmt 

of  i  ,000  million  in  the  White,  Nile  reterv 

back  in  Lake  Albert  till  it  was  wanted. 

Thus,  in  a  bad  year,  the  White  Nile  reservoir  and  the  Sudd  re;;ioii 
economy  would  together  supply  (2,000  -f  4,400  =)  6,400  million  cubic 
metres,  or  about  3,000  millions  less  than  the  full  estimate  ol  9,555 

million  . 

I  ..ike  Albert  is  relied  upon  by  the  1*.  W.  Ministry  to  make  good  the 
balance—"  to  ensure  mil.  lent  water  to  meet  the  ultimate  requirement^ 
of  Egypt  under  the  fullest  cultivation."  The  possibilities  of  storage  in 
Lake  Albert  were  diM  n-.ed  m  /'//<•  l-lu^ineer  of  September  j.jnl.  I-JDJ 
1  1  ins  no  doubt  enorm«>n,  rapacity  as  a  storage  reservoir,  but  the 
effective  storage  possibilities  are  limited  to  what  evaporation  spates  (>! 
the  run-off  of  the  rainfall.  Sir  William  Garstin,  in  his  "  Report  on  the 
lUsin  of  the  I'pper  Nile  "  (igo.j),  states  that  "  the  mean  dist  iiar;;e  o! 
the  Bahr-el-Gebel,  at  Wadelai,  as  worked  out  by  Mr.  Craig,  is  70.)  metres 
<  nbe  p.i  ,,vond  This  equals  a  total  of  some  24,250,000,000  metres 
cube  per  annum."  Now,  the  winter  and  summer  discharges  of  the 
Blue  Nile  are  allotted  to  the  Sudan.  Moreover,  a  minimum  discharge 
from  Lake  Albert  of  25  million  cubic  metres  a  day,  or  287  cubic  metres 
a  second,  is  required  to  provide  for  navigation.  If  the  remainder  — 
482  cubic  metres  a  second  —  is  retained  in  the  lake  during  the  120  days 
ol  ilo,,d,  the  amount  stored  would  be  5,000  million  cubic  metres,  and 
tin  ,  eould  be  reserved  for  use  in  Egypt  during  the  245  days  of  winter 
an.  I  MI  miner.  Allowmj;  for  30  per  cent,  of  loss  on  the  way,  the  amount 
that  \\onld  reach  I  :,\  pt  would  be  3,500  million  cubic  metres. 

So,  if  the  oihci.il  (innate  of  9,555  million  cubic  metres  i  ,  a  correct 
om.  it  appears  that  the  storage  possibilities  of  the  equatorial  lakes  are 
not  much  more  than  sufficient  to  meet  the  balance  of  the  ultimate 
i  e.  |  m  i  (  meats  of  Egypt  —  the  conclusion  arrived  at  on  page  57. 

Note  6  to  page  52.  *  The  White  Nile  Reservoir. 

A  project  for  storage  of  water  on  the  White  Nile  has  been  approved. 
The  general  lines  of  the  project  were  described  on  pages  702  and  704  of 

the  third  edition   (101  0  of  "  Kpyptian  Irrigation,"  by  Willcocks  and 

A  bana^e  i.-,  to  he  built  oil  the  \\lnle  Nile  at  C'.ebel  Auli,  about 


1  \\enty  miles  upstream  of  Khartoum,  In  form  ;i  reservoir  of  a  not. 
capacity  <>f  about  .t.ooo  million  cubic  metres.  (The  complete  M  heme 
also  contemplated  another  barrage  a.l  (iebelcm,  .-.till  higher  up  the  livCT, 
which,  apparently,  is  not  iiu  hided  in  the  project  as  at  present  appi  <  >\ ed.) 
This  storage  scheme  I. ikes  advantage  of  the  peculiar  conditions  \\hich 
exist  in  the  tail  reaches  of  the  White  Nile  during  the  flood  season. 
When  the  nine  Nile  is  in  Hood  and  rising,  it  fills  the  whole  (rough  of  UK; 
Nile  below  Khartoum  and  holds  up  the  White  Nile  water,  and  all.  or 
mo, t  of,  the  water  of  the  White  Nile  is  stored  in  the  natural  re:  ei  voir 
formed  by  ihe  valley  through  which  it  Mows.  In  pioportion  as  the 
I'.lue  Nile  Hood  subsides  the  water  stored  in  the  White  Nile  valle\  ,idds 
itself  to  the  river  discharge  Mowing  forward  io  Kgypt.  In  consequence, 
the  subsidence  of  the  Hood  in  l-'gvpt  is  retarded  sometimes  to  an  extent 
which  is  injurious,  or  even  dangerous.  The  projected  barrage  at  ( iebel 
Auh  will  remain  open  during  the  rising  Hood  while  the  Hlue  Nile  is  hold 
ing  up  the  White  Nile  ;  but,  as  soon  as  the  rise  ceases  and  the  White 
Nile  water  begins  to  move  forward,  the  barrage  will  be  closed  against  it 
and  the  accumulated  water  be  retained  for  use  later  on.  1'y  this  scheme 
two  a.d\antages  are  secured  :  the  period  of  danger  to  Egypt  in  a  ln;;li 
Hood  is  shortened  by  the  fall  of  the  river  being  accelerated  ;  and  a 
valuable  quantity  of  water  is  kept  in  hand  until  the  time  of  need. 

Note  7  to  page  01.     The  Triple  Canal  System  of  the  Punjab. 

In  the  Government  of  India's  Review  of  Irrigation  for  1916-17 
the  completion  of  the  Triple  Canal  Project,  so  far  as  the  main  canals 
are  concerned,  was  announced. 

"The  Triple  Canal  Project  was  commenced  in  1905;  of  its  three 
component  parts  the  Upper  Chenab  Canal  was  opened  in  £912,  the 
Lower  Bari  Doab  in  1913,  and  the  Upper  Jhelum  in  KM 5.  .  .  .  The 
Upper  Chenab  Canal,  with  a  bed  width  of  240  feet,  a  full  supply  depth  of 
12  feet,  and  a  capacity  of  11,700  cubic  feet  per  second  is,  it  is  believed, 
the  largest  irrigating  channel  in  the  world." 

'The  cost  of  execution  of  the  project:  is,  in  round  numbers,  £7,000,000. 
If  the  annual  irrigation  reaches  2,000,000  acres,  which  it  is  not  unlikely 
to  do,  the  net  revenue  will  be  nearly  £560,000,  and  the  return  on  the 
capital  cost,  will  become  cS  per  cent. 

Note  8  to  page  176.     Canal  Sections. 

There  are  other  considerations,  besides  the  prevention  of  scour  and 
deposit  of  silt,  to  be  borne  in  mind  when  canals  are  being  designed.  The 
following  passage  occurs  in  a.  paragraph  dealing  with  "  Seepage  Losses 
in  Canals  "  in  the  Report  of  the  Ministry  of  Public  Works,  Kgypt,  for 
1914—1915  :— 

"  The  experiments  indicate  that  although  wide  shallow  canals  may 
silt  less,  yet  the  loss  by  seepage  in  them  is  greater  than  in  narrow  and 
deep  canals,  the  seepage  being  directly  proportional  to  the  width  and 
wetted  perimeter,  but  proportional  only  to  the  square  root  of  the 
hydraulic  mean  depth.  This  factor  should  inllucncc  canal  design  in 


286  APPENDIX. 

Lower  Egypt  where  eventually  large  areas  will  be  drained  by  lift,  so 
that  seepage  losses  should  be  jealously  guarded  against." 

Note  9  to  page  245.     River  protective  and  training  works. 

Sir  John  Ottley,  K.C.I.E.,  formerly  Inspector-General  of  Irrigation 
in  India,  in  a  review  of  the  first  edition  of  this  book  in  the  R.E.  Pro- 
fessional Papers  of  July,  1907,  considers  the  distinction  made  between 
protective  and  training  works  as  "  somewhat  fanciful,"  and  is  not  a 
believer  in  powers  of  persuasion.  He  writes  :  "  It  is  quite  certain  that 
those  officers  in  Northern  India  who  have  the  largest  experience  in 
river  work  are  of  one  mind  in  agreeing  with  Mr.  Good  that  a  river  should 
be  '  fought  and  not  merely  tickled.'  For  ten  or  twelve  years  prior  to 
1887  '  persuasion  '  was  tried  at  Narora  and  miserably  failed  ;  since 
1887  the  Ganges  has  been  '  fought '  with  conspicuous  success  and  at  no 
greater  an  expenditure  of  money  than  before." 

Note  10  to  page  252.     The  cotton  crop  of  Egypt. 

The  passage  to  which  this  is  a  note  was  written  in  1907  as  it  stands 
now.  The  Report  of  the  Ministry  of  Public  Works,  Egypt,  for  1911 
(published  1913),  contains  this  paragraph  from  the  pen  of  the  Under 
Secretary  of  State  : — 

"  It  is  extremely  likely  that  in  the  case  of  1909  it  was  not  the  removal 
of  the  Sharaqi  Decree  itself  at  an  early  date,  but  the  superabundance  of 
water  at  the  disposal  of  the  cultivators  and  the  high  levels  in  the  canals, 
which  they  so  freely  took  advantage  of,  which  did  the  damage  to  that 
year's  cotton  crop.  In  future  years  it  is  the  intention  of  the  Depart- 
ment to  pass  down  main  canals  at  this  period  of  the  year  just  sufficient 
to  meet  requirements.  Any  excess  over  this  quantity  will  be  passed 
into  the  river  channels  and  allowed  to  flow  to  the  sea." 

This  points  the  moral  drawn  on  page  252. 

The  cotton  crop  of  1909 — a  year  of  high  summer  river  discharges 
exclusive  of  the  reservoir  addition — yielded  5,000,772  kantars,  being  at 
the  rate  of  3-24  kantars  per  acre  of  crop  ;  whereas  the  crop  of  1900 — the 
year  of  the  lowest  summer  supply  in  the  river  on  record  and  without  a 
reservoir  to  help — yielded  5,427,339  kantars,  being  at  the  rate  of 
4.42  per  acre  of  crop. 

In  the  Report  of  the  P.  W.,  Egypt,  for  1912  (published  1914)  a 
table  is  given  showing  the  areas  planted  with  cotton  and  the  yield  for 
each  year  from  1891  to  1912.  From  the  figures  therein  given  it  appears 
that,  since  the  Assuan  reservoir  first  came  into  action  in  1903,  the  area 
of  cotton  crop  has  increased  by  one-third,  whereas  the  total  yield  has 
increased  by  one-sixth  only  ;  and  the  yield  per  acre  has  decreased  from 
an  average  of  5  kantars  an  acre  to  4' 3.  Since  1912  the  cotton  crop 
returns  show  no  improvement.  The  1915  and  1916  crops  yielded  results 
inferior  to  those  of  the  1900  crop  as  regards  both  the  total  yield  and  the 
yield  per  acre  of  crop. 


INDEX. 


A. 


ABSORPTION  by  soils,  31,  65  ;  in  basins, 
21,  22  ;  in  canals,  35,  216  ;  in  reser- 
voirs, 41,  70,  71  ;  in  the  Nile  marshes, 
52— 55  ;  in  transit  from  reservoir,  48, 

64 

Abu  Bagara  Canal,  Egypt,  18 

Abyssinia,  region  of  rainfall,  2 

Acre- foot,  33,  34 

Administration  of  canals,  America,  232, 
233  ;  France,  232  ;  Spain,  231 

Afflux  above  river  weirs,  112 

African  takes,  46 

Africa,  South,  storage,  59,  63  ;  de- 
velopment, 59,  63 

Agriculture  and  irrigation,  30,  250,  251, 
252 

Albert  Edward  Nyanza,  46 

Albert  Nyanza,  46,  54,  55,  56,  57 

Alexandria,  Mex  pumping  station,  256 

Algeria,  Khamis  undersluice,  93  ;  silt- 
ing up  of  reservoirs,  92 

Alicante  dam,  92,  102  ;  water  rates,  228 

Alignment  of  channels,  171,  172  ;  dams, 
91;  drains,  173;  river  weir,  114; 
"Sudd"  channel,  55 

Almanza  dam,  82,  102 ;  water  rates,  228 

America,  canal  administration,  232,  233  ; 
capacity  of  reservoir,  33  ;  Chamoine 
system  in,  108 ;  "  duty  "  of  water,  32  ; 
inland  waterways,  259  ;  irrigation, 
108  ;  new  Croton  dam,  103 ;  river 
banks,  240 ;  water  rates,  227  ;  Western 
States,  development,  63 ;  windmills, 
106 

American  dams,  71,  79;  type  of  river 
regulator,  108 


Andalucia,  Spain,  172 

Anicut,  Coleroon,  135  ;  Grand,  29,  in  ; 
Indian  type  of  weir,  107  ;  site  of,  113  : 
sluices,  112,  113;  Sone,  113 

Anicuts,  silt  deposit  above,  112,  113, 
114 

Apparatus,  lifting,  43 

Apron,  protective,  Assuan  dam,  100 

Aprons  of  clay,  130,  132;  escapes,  197; 
impermeable,  130 

Aqueduct,  Nadrai,  67,  68 

Aqueducts  of  iron,  207  ;  of  wood,  207  ; 
over  drainages,  203 — 206 

Area,  catchment,  31  ;  cultivable.  Egypt, 
7  ;  irrigable,  212  ;  irrigated  by  Divi 
pumps,  139,  257  ;  irrigated,  India,  8  ; 
Komombos  scheme,  139  ;  of  arid  re- 
gions, U.S.A.,  9  ;  of  crop,  limitation 
of,  213,  218,  222,  223  ;  of  crop,  rate 
on,  213,  215;  of  crop  sown,  41;  of 
Dongola  province,  105;  of  drainage 
served  per  pump,  257  ;  of  Egypt,  50 ; 
of  Lake  Albert,  56  ;  of  Lake  Moeris, 
47  ;  of  St.  Lawrence  lakes,  45,  46  :  of 
tanks,  India,  61, 62  ;  under  well  irriga 
tion,  43,  44 

Areas  commanded,  178  ;  gross,  178  ; 
inundated,  Egypt  and  India,  25,  26 ; 
irrigated  by  pumps,  138,  139  ;  irrigated 
by  tanks,  62  ;  irrigated,  India,  62  ;  of 
cultivation,  33  ;  of  lakes,  46  ;  un 
flooded,  1 8 

Arid  conditions,  2 ;  regions  of  Canada, 
9  ;  regions  of  Mexico,  9 ;  regions  ot 
U.S.A.,  9,  58 

Arid  regions,  U.S.A.,  require  storage, 
58  ;  west  of  U.S.A.,  windmills,  105, 
106 


288 


INDEX. 


Arizona,  ancient  irrigation  works,  30  ; 
miner's  inch,  34 

Armant  pumping  station,  138 

Artesian  wells,  44 

Ashlar  covering  for  floors,  116,  141,  142  ; 
covering  of  Delta  barrage  floor,  130; 
floor  below  falls,  195 

Assessment,  land  tax,  226,  227 

Assessment  of  water  rates,  213 

Assiout  barrage  design,  127,  131 — 133, 
149  ;  floor,  142  ;  foundations,  145, 
149,  150;  piles,  151,  155 

Assiout,  head  sluice  above  barrage,  192 

Association  of  cultivators,  232 

Assuan  dam  and  reservoir,  50,  51  ;  de- 
scribed, 96 — 100  ;  effect  of,  incom- 
plete, 7  ;  Egypt's  requirements  before 
making,  56  ;  locks,  262,  263,  265,  266  ; 
maximum  pressure,  102  ;  of  necessity 
of  masonry,  80  ;  raising  of,  52,  99, 
100  ;  results  of  building,  28 

Assuan  reservoir  and  cotton  crop,  251, 
252  ;  and  dam,  51,  52  ;  capacity,  56, 
70 ;  described,  97,  98,  99 

Atcherley's  theory  of  dam  stresses,  81, 
100 

Atfeh  pumping  station,  135 — 138 

Australia,  Mundaring  dam,  88,  102,  103 

Ayat  pumping  station,  138 

B. 

BABYLON  and  irrigation,  4,  5,  29 
Babylonia  and  irrigation,  3,  4,  7,  28 
Backing  up  of  water,  or  afflux,  112 
Baikal  lake  and  Yenisei  river,  46 
Baird-Smith,  Capt.R.,on  Italian  "  duty," 

38 

Baiturnee  weir,  1 14 
Baker,  Sir  B.,  on  dam  designs,  81,  82 
Baltic  and  river  navigation,  47 
Banks.     See  also  Embankments 
Banks,    basin,   cuts    in,    15  ;    cross,    of 
basins,    21  ;    dimensions  of,    24,   25  ; 
enclosing  foundation  area,    143,  145  ; 
longitudinal,  15  ;  protection  of  slopes 
of,  24  ;  protective,  14,  237 — 243  ;  pro- 
tective, action  of,  13 
Bari  Doab  canal,   "duty"  on,  41  ;  loss 

of  water,  35 
Barrage,   Assiout,  127,    131—133,  142; 


Delta,   ill,   116,  128—130,  135,  137; 

Delta,    restoration,    127,    130,    136  ; 

Egyptian   type   of  weir,    107  ;    Zifta, 

131—134,  142  ;  Zifta,  floor,  142 
Barrages  of  Egypt,  112,  134 
Base  of  "  duty  "  of  water,  40,  41 
Bascule  girders,  262,  263 
Basin  banks,  cuts   in,    15  ;    dimensions, 

24,  25  ;  protection  of  slopes,  24 
Basin  crops,  24,  28 

Basin  escape  design  and  discharge,  22,  23 
Basin  escapes,  15—17,  21 — 24,  194,  197 
Basin  feeder,  head  and  off-take,  19—24  ; 

silting  of  head  of,  21  ;  syphon  under, 

21,  22  ;  work  of,  16,  17,  18 
Basin  filling,  23,  24 
Basin  inundation,  depth  of,  20,  22 
Basin  land  conversion,  28  :  value  of,  28 
Basin  regulator  design,  23,  192,  193 
Basin  regulators,  15,  16,  17,  21 
Basin  system,  3,  15,  16,  17,  29 
Basin    system,    Egypt,    26 ;    high    level 

canal,   16,   18  ;  principles  of  working, 

1 6,  23 ;  project  for,  19  ;    sluices,  21 ; 

supply,  16,  17;  syphon  canal,  16,  18 
Basins,  contents  of,  21 ;  deposit  of  silt, 

16;  emptying,  23,  24;  feeder-sluices, 

17;  period  of  emptying,   19,  20,  22; 

period  of  filling,  19,  20,  22 ;  size  of, 

20 ;  sluices,  21 
Batter  of  lock  walls,  265 
Bear  Valley  dam,  92,  93 
Belgium,  inland  waterways,  259 
Bench  flumes,  207 
Bengal  crops,  37 
Beresford's  filter,  124,  125 
Betwa  dam,  82,  84 
Bhatgarh  dam,  95,  96,  100,  102 
Bhatgarh  reservoir,  97 
Blue  Nile  in  Abyssinia,  2 
Bombay,  consolidated  rate,  227  ;  Deccan 

districts,  58  ;  Maladevi  tank  dam,  73  ; 

Orissa  and  Midnapore  canal  systems, 

258  ;  waste  weirs  of  reservoirs,  69 
Books  of  reference,  278 — 281 
Bor,  the  Nile  at,  55 
Boul6  shutters,  107,  108 
Brahmini  weir,  114 
Branch    canal    discharges,     1851     head 

sluices,  192 


INDEX. 


289 


Branch  canals,  171,  180;  184 

Branch  drains,  187,  188,  189 

Breach  in  banks,  241,  242 

Buckley,  Mr.  R.  B.,  on  canal  discharges, 
177,  178;  on  the  Chenab  canal,  f  ', 
on  the  Coleroon  anicut,  134,  135  ;  on 
the  Delta  barrage  weir,  124  ;  on 
"duty"  of  water,  41,  42  ;  on  "duty" 
for  Spain,  39 ;  on  flow-off,  65  ;  on 
navigable  waterways,  India,  258  :  on 
Narora  weir  failure,  1 18,  J 19  ;  on  rota- 
tions, 217  ;  on  the  Trebeni  canal  head 
sluice,  190,  191 

Budki  superpassage,  205 

Burmah,  consolidated  rate,  227  ;  Thap- 
angaing  aqueduct,  206 

Burra  weir,  1 14 

Bywash  of  reservoir,  67 

Bywashes  in  basins,  15 


C. 

CACHE-LA-POUDRE  valley,  Colorado,  60 
California,  curved  dams,  92  ;  "  duty  "  of 
water,    39 ;     miner's   inch,    34  ;     San 
Diego  flume,  207 ;    Southern,    dams, 
79  ;  Turlock  and  Modesto  districts,  9; 
Turlock  dam,  84  ;  wells,  44 
Camere"  curtain,  107,  108,  202 
Canada,   arid  regions   of,  9  ;    Western, 

development,  63 

Canal,  Abu  Bagara,  Egypt,  18  ;  adminis- 
tration, America,  232,  233  ;  adminis- 
tration, France,  232  ;  and  well  water 
compared,  44,  45  ;  Bari  Doab,  loss  of 
water  on,  35  ;  Bari  Doab,  '  *  duty  "  of 
water  on,  41  ;  branch,  alignment,  171  ; 
Chenab,  effect  of  making,  7  ;  Chenab, 
exceptional  case,  8 ;  cross-sections, 
178,  179;  dimensions,  178,  179;  dis- 
charges, 177,  178;  escapes,  192—194, 
197  ;  falls,  177,  192,  195—197.  260 
Canal,  flood,  design  of,  20,  21  ;  Ganges, 
loss  of  water  on,  35  ;  gradient,  173, 
177;  head,  "duty"  at,  41;  head 
sluice,  174,  190—192 ;  high  level, 
basin  system,  16,  18;  irrigation  area, 
India,  6.2  ;  loss  of  water  in,  35,  36 ; 
Mahmudia,  137 ;  Main,  alignment, 
171;  of  Babylon,  29;  of  Hammurabi, 
I. 


4,  29 ;  project  and  evolution  of  scheme, 
30 ;  spurs,  244,  245 ;  syphon,  basin 
system,  16,  18 ;  system  described, 
171  ;  system,  design,  48 ;  weirs,  set 
canal  falls ;  works,  neglect  of,  4 ; 
velocity,  173— 177 

Canals,  alignment  of,  171,  172;  basin, 
Egypt,  26  ;  flood,  25,  26 ;  inundation, 
relieving  pumping  stations,  138;  Meso- 
potamia, 4 ;  of  inundation  in  basin 
systems,  14,  15  ;  of  inundation.  India, 
25,  26 

Capacity,  Assuan  reservoir,  97,  98,  99  ; 
Bhatgarh  reservoir,  97 ;  Marikanave 
reservoir,  89,  90,  91  ;  of  Albei  t  Nyanza, 
56 ;  of  drains,  187,  188,  189  ;  of 
reservoirs,  how  determined,  70  ;  of 
reservoirs,  how  expressed,  33 

Cape  Colony,  South  Africa,  26,  27 

Cascades  on  canals  or  escape  channels, 
194,  196 

Caspian  and  river  navigation,  47 

Castellon,  land  values,  1 1 

Cast-iron  piles,  151,  152,  155 

Castlewood  reservoir  dam,  79,  80 

Catalonia,  water  rates,  228 

Catchment  and  flow-off",  59,  66 — 68  ; 
and  rainfall,  43,  67,  68 ;  areas,  2,  31, 
58  ;  discharge  formulas,  69;  diversion 
of  supply  of  one  to  another,  59,  60,  6 1  ; 
of  reservoir,  63,  64,  65  ;  Periyar,  60  ; 
position  and  nature  of,  45 

Cauvery  river  weir,  29 

Cement  grout  used  for  closure  of  springs, 
150;  used  for  pipe  syphon  ends,  168, 
169 

Cement  grouting,  advantages  of,  163  ; 
apparatus,  152,  156,  158,  159;  at  the 
Delta  barrage,  157,  158,  159;  for 
foundations,  157 — 163,  166,  167  ; 
joints,  Detroit  tunnel,  170 ;  of  the 
Delta  barrage  foundations,  163,  164, 
165  ;  Shubra,  156,  157,  166,  167 

Cement,  proportion  in  grouted  masonry, 
161 

Central  Provinces,  India,  rainfall,  2 

Chain  of  basins,  15,  16,  18 

Chaldea  and  irrigation,  3,  4,  5 

Chamber  of  locks,  261  ;  walls  of  locks, 
264,  265 

U 


290 


INDEX. 


Chamoine  system  of  closure,  108 

Channel  through  Nile  swamp>,  55,  56,  57 

Channels,  classification  of,  171 

Channels,  underground,  43 

Charles  III.  of  Spain,  dams  built  in  reign 
of,  II 

Chenab  Canal,  effect  of,  7  ;  exceptional 
case,  8;  notch  falls,  198,  199;  river, 
25,  61  :  weir,  114,  116,  121,  122 

Classification  of  dams,  71 

Clay  apron,  130,  132 

Closure  by  horizontals,  200,  201 ;  by 
iron  gates,  2OI,  202 ;  by  roller  curtains, 
202  ;  by  vertical  needles,  200 ;  of  Delta 
barrage  gates,  137 

Coleroon  anicut,  135 

Collins,  Mr.  M.  R.,  on  land  values, 
Transvaal,  9 

Colorado,  ancient  irrigation  works,  30 ; 
diversion  of  flow-off,  59,  60  ;  Castle- 
wood  reservoir  dam,  79,  80;  "duty" 
of  water,  39 ;  High  Line  canal, 
207 

Commanded  areas,  178 
Commander  Felix  Jones  on  Mesop  >tamia, 

5 

Commission,  Indian  irrigation,  58 
Como,  Lake,  46 

Compressed  air  for  foundations,  153 
Concessions  for  irrigation,  Spain,  232 
Concrete  bed  of  pipe  syphons,  211 
Concrete  casing  of  pipe  syphons,  211 
Conflict  of  irrigation  and  navigation,  259 
Congo,  lake  source  of  river,  46 
Consolidated  land  and  water  rate,  227 
Consorzio  of  Piedmont,  231 
Constance,  Lake,  46 
Construction  works,  141 
Control  of  irrigation  by  Government,  228, 

232 

Core  of  steel  plate,  79 
Core  wall  of  weir,  foundations  of,  154 
Core  walls  in  dams,  71,  75 — 79 
Cost  of  Delta  barrage  restoration,  136  ; 
of  Divi  pumping  station,  257  ;  of  land 
owners'     operations,     250,     251  ;     ol 
lifting    water,    139,    140;    of   lifting 
water,  Divi  island.  257 ;  of  pumping 
136,    256,    257;   of  pumps,    136;    of 
working  Delta  barrage,  136 


otton  rrop,  251,  252 
Cotton  crop,  Egypt,  7 
Cotton,  water  allowance,  218,  222; 

watering  intervals,  218,  221 
Cotton,  Sir  A.,  and  navigation,  258 
Country  slope,  173,  177 
rib  weir,  109 

rop  area,  sown,  41  ;  gross,  Egypt,  37 ; 
rate  on,  213,  215 
Crop  areas  irrigated  by  machines,    105, 

1 06 

Crop,  cotton,  Egypt,  7;  flood,  Egypt, 
38  ;  maize,  Egypt,  7  ;  rice,  Egypt,  37  ; 
rice,  India,  38;  value  of  cotton,  136 
Crops,  basin,  24,  28  ;  Bengal,  37  ;  cost  of 
raising,  Egypt,  7  ;  double,  remark  by 
Megasthenes,  7;  Egypt,  37;  Egypt, 
after  flood,  3 ;  Egypt,  entirely  depen- 
dent on  irrigation,  8  ;  flood  season,  25  ; 
hay,  France,  10 ;  insurance  of,  31  ; 
kharif  and  rabi,  25,  26,  37  ;  perennially 
irrigated,  28;  Punjab,  37;  requiring 
summer  waterings,  63  ;  saved  by  irriga- 
tion, value  of,  8  ;  summer,  28  ;  under 
irrigation,  31  ;  United  Provinces, 
India,  37;  value  of,  28;  value  of, 
India,  8;  waterings,  34,  36,  37; 
winter,  28 

Crest  shutters,  100,  112,  113,  123,  125 
Cross  banks,  21 

Cross  embankments,  regulators  of,  23 
Cross  section  of  canals,  178,  179 
Croton  dam,  90,  91,  100 
Cultivable  area,  Egypt,  7 
Cultivators  and  irrigation,  251 
Culverts  in  river  banks,  242 
Curtains  of  sheet  piling,  151 
Curtain  walls,  115,  121,  153,  154 
Curtain  wells,  120,  121,  122 
"  Cusec,"  abbreviation,  32 
Cushion  below  drop  wall,  1 119 
Cuts  in  basin  banks,  15 

D. 

DABAYA,  pumping  station,  138 

Dam,  Alicante,   82,  92,  102;  Almanza, 

82,    102;  Assuan,   7,   28,  50,  51,  52. 

56,  96—100,  102  ;  Bear  Valley,  92,  93; 

Betwa,  82,  84;  Bhatgarh.  95,  96,  100, 

102 ;    Castlewood   reservoir,    79,   80 ; 


INDEX. 


291 


Croton,  90,  91,  100  ;  Foy  Sngar  tank, 
77,  80  ;  Furens,  82,  87,  88,  91 ;  Genii 
river,  109  ;  Gros  Bois,  102  ;  Kair 
tank,  77,  78  ;  La  Grange,  83, 

84  ;  Maladevi  tank,   73,  75 ;  Marika- 
nave,  89,   90,    102,    103;  Mundaring, 
88,   102,    103 ;  New  Croton,  76,  102, 
103  ;  Nira,   86,  88  ;    Periyar,  60,  88, 
89;  Quaker  Bridge,   91,  102;  Sweet- 
water,  92  ;  Titicus,  91  ;  Turlock,  84, 

85  ;  Upper  Otay,  92  ;  Val  de  Infierno, 
92,  98  ;  Verdon,  102  ;  Vyrnwy,  84,  85, 
86 ;    Walnut     Grove,    79  ;    Zola,    92, 

93 

Damietta  branch,  137,  138,  238  ;  branch 

weir,  131  ;  flood  level,  239 
Dams,  alignment  of,  91  ;  American,  79  i 
core  walls,  77  ;  earthen,  South  Africa, 
26  ;  flanks  of,  76  ;  foundations  of,  71, 
73«  75  5  Government  work,  236 ; 
height  of,  59  ;  insubmergible,  71,  80, 
83,  100  ;  limits  to  height,  70  ;  loose- 
rock,  71, 79,  80;  of  different  types,  71  ; 
of  earth,  71—74.  78  ;  of  masonry,  71, 
72,  78,  80  ;  of  reservoirs,  57,  58,  59  ; 
of  South  California,  79;  of  Spain,  II, 
82  ;  on  rivers,  106,  107  ;  pierced,  71, 
80;  Poire'e,  107;  pressures  in,  102; 
rockfill,  71,  79>  80;  "saai,"  27; 
scouring  sluices  of,  92 — 96  ;  solid,  71, 
80;  stability  of,  81 ;  stresses  in,  81 ; 
submergible,  71,  80,  83,  100 ;  tem- 
porary, Nile,  137  ;  theory  of  construc- 
tion, 8 1  ;  waste- weirs  and  outlets,  76  ; 
water  cushion,  83,  84,  85  ;  with  and 
without  cores,  71 ;  with  curved  plan, 
91,  92 

Darro  river,  Granada,  109 
Deacon,  Dr.,  on  Vyrnwy  dam,  86 
Deccan  districts  of  Bombay,  storage,  58 
Delta  barrage,  Egypt,   in,   116,    128— 
130.  J35»  !37,    H5  J  cement  grouting 
at,    157.   158,    159 ;  grouting  founda- 
tions of,    163,   164,  165  ;  restoration, 
127,  130,  136,  145—147  ;  water  levels, 
132  ;  weirs,  114,  122 — 125 
Delta  of  Egypt,  and  Lake  Moeris,  29, 
48  ;  and  water  distribution,  128,  131  ; 
drainage,     1 36 ;    flood    levels,     238 ; 
formation  of,    13  ;  irrigation  of,  135, 


136,  138  ;  training  river  at  apex  of, 
247 

Deltaic  branches  of  Nile,  29,  48  ;  river 
regulator  of,  no 

Deltaic  formation,  13  ;  river  banks,  237 

Deltas  of  rivers,  growth  by  deposit,  12; 
low  seaward  margins,  253  ;  of  India, 
formation,  13 

Demak,  Java,  rotations,  223 

Demand,  accommodation  of  supply  to. 
64  ;  and  supply,  67  ;  for  water,  31,  32. 
49 

De  Meyier,  Mr.  J.  E.,  on  rotation,  Java, 
223,  224,  225 

Deposit.     See  also  Silt 

Deposit  of  silt,  24,  25,  173—177,  217; 
in  basins,  16 ;  in  reservoirs,  98,  92, 
95,  96  ;  locks,  264 

Deposit,  silt,  staunching  action  of,  35 

Deposition  of  silt,  12,  13,  248 

Deposits  in  canals,  244,  245 

Design  of  canal  system,  48  ;  of  canal 
works,  192 

Detroit  river  tunnel,  169,  170 

Dickens'  formula,  69 

Diesel  oil  engines,  139 

Dimensions  of  canals,  178,  179;  ol 
drains,  186—189 

Discharge  determined  by  crop  and 
"duty,"  212;  formulas  for  catch- 
ments, 69  ;  from  tanks  and  reservoirs, 
69,  70  ;  measurements,  275,  276,  277  ; 
Nile,  50;  of  basin  escapes,  22,  23; 
of  basin  feeder,  21  ;  of  branch  canals, 
185  ;  of  Divi  pumping  station,  257  ; 
of  drainages,  206 ;  of  Kosheshah 
escape,  194  ;  of  lock  sluices,  262,  263 ; 
of  main  canals,  185 

Discharge  of  reservoir  escape,  67  ;  of  St. 
Lawrence  lakes,  46 ;  Periyar  river, 
61  ;  required,  36,  37,  38 ;  required  by 
Egypt,  50,  51 

Discharges,  flood,  68  ;  flood,  Egypt,  38  ; 
lake,  32  ;  of  canals,  177,  178;  of  dis- 
tributaries, 180.  181,  184,  185 ;  of 
drains,  187,  188,  189  ;  record  of,  68  ; 
required,  40 ;  river,  31  ;  summer, 
Egypt,  38 ;  through  the  "  Sudd, '' 

53,  54 
Discharging  capacity  of  river,  238 

U  2 


292 


INDEX. 


Distributaries  of  a  canal  system,  180— 
185  ;  alignment  of,  171  ;  rotation  by, 
217 

Distributary  cross  -  section,  182  ;  dis- 
charges, 180,  181,  184,  185  :  loss  of 
water  in,  35 

Distribution  according  to  area,  213,  215  ; 
affects  "  duty,"  212  ;  by  rotation,  180, 
181,    183,   184;  means  of,   171—189; 
methods  of,  180,   212—226 ;  of  flood- 
water,  16,  17 ;  skill  in,  affects  loss,  35  ; 
with  convenient  surface  levels,  38 
Distribution  works,  190 — 21 1 
Diversion  from  one  catchment  to  another, 

59,  60,  6 1 

Divi  pumping  project,  140,  257 
Dongola  irrigated  by  sakias,  104 
Drainage  and  irrigation,  172,  182,  183, 
185,  186 ;  by  free-flow,  255  ;  by 
pumps,  257  ;  crossings,  203—208 ; 
diverted,  203  ;  East  of  United  States, 
46 ;  inlets,  203  ;  in  super-passages, 
203 — 205,  209  ;  of  Delta  of  Egypt, 
186  ;  of  earthen  dams,  74  ;  passed  by 
level  crossing,  203,  204,  206,  207 ; 
pumping  for,  256,  257  ;  subsoil,  253, 
254.  255  ;  syphons,  203,  204,  208  — 
211  ;  under  aqueducts,  203 — 206 
Drains,  alignment,  173  ;  of  a  canal 
system,  185 — 189  ;  overworked,  252  ; 
reclamation  by,  253,  255  ;  relief  of, 
under  rotation  system,  183  ;  scheme 
of,  31 

Dredging  drains,  189 
Drought,  years  of,  India,  8 
Duties  of  Government  engineers,    228, 

229 

"Duty"  of  water,  America,  32 ;  as 
affected  by  rain,  42  ;  at  head  of  canal, 
41  ;  at  reservoir,  41  ;  base  of,  40,  41  ; 
basis  of  project,  34  ;  calculation  of, 
34  ;  California,  39  ;  Colorado,  39  ; 
definition  of,  32 ;  depends  on  manner 
of  distribution,  212  ;  determination  of, 
250 :  during  rotations,  42  ;  Egypt, 
33.  34,  37—39.  42,  220,  252  ;  equiva- 
lent expressions,  268 ;  for  kharif, 
India,  39  ;  for  rabi,  India,  41  ;  from 
life  period  of  crop,  42  ;  high  or  low, 
34  ;  India  32,  33,  36—38  ;  in  irriga- 


tion, 32—42  ;  in  terms  of  area,  32— 
34,  36  ;  in  terms  of  discharge,  32 — 34, 
36  ;  in  terms  of  volume,  32 — 34 
Italy,  38  ;  Montana,  39  ;  of  period  of 
pressuie,  41,  42  ;  of  reservoir,  33,  40  ; 
of  whole  season,  42  ;  on  Bari  Doab 
canal,  41  ;  rice,  38  ;  shown  in  annual 
reports,  41  ;  South  of  Europe,  33  ; 
South  of  France,  39;  Spain,  39; 
unit  of  measure,  32  :  Utah,  39 
Dwarf  walls  below  escapes,  197 


EARTHEN  dams,  71—74,  78 
Economy  of  water,  2(6,  261,  262 
Egypt,  Abu  Bagara  Canal,   18;   ancient 
irrigation,  7  ;  and  Mesopotamia,  floods 
compared,  3  ;  area,  50  ;  as  affected  by 
lakes,   46  ;    as  illustrating  principles, 
181 ;     Assuan    dam,    96 — 100,    102 ; 
Assuan  reservoir  capacity,  70  ;  Atfeh 
pumps,     137,     138;     barrages,     134; 
basin  banks,  24,  25  ;  basin  canals,  26 ; 
basin  system.  3,  26  ;  canal  discharges, 
184,  185  ;    capacity  of  reservoir,  33  ; 
capital  expenditure,  7  ;  corn,  3  ;  cost 
of  raising  crops,   7  ;  cotton  crop,   7, 
251,  252  ;  crops  after  flood,  3  ;  crops 
entirely   dependent   on   irrigation,   8  ; 
crops,  summer,  37  ;  cultivable  area,  7  ; 
decay  of  irrigation  works  of,  6 ;  delta 
of,  29,   48;  Delta  barrage,    in,   116  ; 
Delta  barrage   weir,     123,    124,    125 ; 
development,  63  ;  discharges,  38  ;  dis- 
charge required,  50,  51  ;  distributaries, 
181,   184,   185  ;  drains  and  drainage, 
136,  186,  188,  189;  "  duty  "  of  water, 
33.  34,  37—39,  42,  252  ;  flood  crop, 
38  ;   flood  discharge   of  canals,    178  ; 
flood      levels     in      delta     of,      238  ; 
flood    season,   3,    38 ;    forced    labour 
abolished,  7  ;  formation  of  delta,  13  ; 
forms   of  spurs,    243,    244 ;    gates   of 
barrages,    127  ;    Government   controls 
{irrigation,     228,      234  ;     granary    of 
Rome,     3 ;    gross,    commanded    and 
crop  areas,  37,  178  ;  horizontal  closing 
plank,   201  ;   inundation   canals,    26  ; 
inundation  in,  25  ;  irrigated  by  flood, 
12  ;  irrigation  by  inundation,  3  ;  Irri 


INDEX. 


293 


gation  Department,  229,  230 ;  irri- 
gation of  delta  of,  135,  136  ;  irrigation 
record  of,  7 ;  Kosheshah  escape,  194, 
195  ;  Lake  Mareotis,  256  ;  Lake 
Tsana  as  reservoir  for,  2  ;  land  tax, 
226;  Lower,  irrigation,  129,  130; 
main  canal  cross-section,  179  ;  maize 
crop,  7  ;  navigable  canals,  259  ;  needle 
closure,  200 ;  Nile,  its  rain-water 
carrier,  43 ;  perennial  irrigation,  29 ; 
period  for  calculating  duty,  42  ;  period 
of  basin  filling,  19,  20,  22  ;  pipe 
syphons,  167  ;  pumps,  106,  139 ; 
rainfall,  2,  3  ;  recent  history,  49 ; 
reclamation  of  river  bed,  248 ;  re- 
cuperation of,  6  ;  reservoir  of,  49,  50  ; 
rice  crop,  37  ;  river  banks,  237,  240, 
241 ;  rotations,  184,  216,  218 — 222; 
size  of  regulator  vents,  191  ;  spurs, 
245,  247  ;  storage  requirements,  55,  56  ; 
summer  season,  104;  the  sakia  of, 
104  ;  the  skadouf  of,  104 ;  training 
works,  47  ;  under  the  Pharaohs,  3,  29!; 
unreclaimed  lands,  253  ;  Upper,  basin 
programme,  23,  24  ;  value  of  land,  7  ; 
water  allowance.  37,  38 ;  watering 
periods,  37,  38  ;  water  rates,  226  ;  water 
supply,  52,  56  ;  waterways  public,  235  ; 
waterwheels,  106 ;  well  irrigation,  43  ; 
yield  of  high  and  low  lands,  255 

Egyptian  barrages,  112  ;  type  of  river 
regulator,  107,  131,  132,  134;  weir, 
114,  123,  124,  125 

Egyptians,  control  of  inundation  by,  3 

Elche,  Moors  first  engineers  of,  10 

Embankments.     See  also  Banks 

Embankments,  cross,  14,  15 ;  cross, 
regulators  of,  23  ;  flood,  237—243 

Encroachment  by  river,  243 

Engineer,  well-irrigation  not  his  pro- 
vince, 44 

Engineering,  irrigation,  scope  for,  9 

England,  rainfall,  I 

Equatorial  lakes,  Africa,  46,  52,  54,  56, 

57 
Erosion,  by  waves,  241  ;  in  canals,  244, 

245;    of  bed  of  watercourse,   12;   of 

toe  of  Assuan  dam,  99  ;  river,  21 
Escape,  basin,  design  and  discharge  of, 

22,  23 ;  by  level  crossing,  22  ;  canal, 


design   of,     192,    193,  194  ;    of  basin 
chain,  22,  24  ;  of  reservoir,  65,  67,  69  ; 
waterway  of  reservoir.  65,  67,  69 
Escapes,  basin,  working  of,  23,  24 ;  oi 
basins,   15,  16,  17,    21,  22,  24;   on  a 
canal  system,  193,  1^4 
Esla  canal,  water  rates,  228 
Euphrates  and  floods,  3,  4,  5,  12 
Europe,  and  Philse,  51  ;  irrigating  coun- 
tries in,  10 ;    natural   reservoirs,    46 ; 
Southern,  "duty"  of  water,  33 
Evaporation  affected  by  temperature,  31  ; 
in  basins,  21,  22  ;  in  canals,  35,  216; 
in  reservoirs,  41,  50,  59,  70,  71  ;  in 
the   Nile    marshes,    47,     52—55 ;    in 
transit    from    reservoir,    48,    64;    on 
catchments,  65 

Expenditure,  annual,  Divi  pumps,  257  ; 
by  landowner,  250,  251  ;  capital, 
EgyPl>  7 ;  capital,  India,  8  ;  profit  on, 
India,  8 

F. 

FAILURE  of  Chenab  weir,  121,  122 ;  of 
Delta  barrage,  128,  129  ;  of  Narora 
weir,  118,  119 

Falls  on  canals,  177,  192,  195,  196, 
260 

Farmers  and  irrigation,  251 

Fayum  and  Lake  Moeris,  29,  47  ;  and 
Wadi  Rayan,  52  ;  waterwheels,  106 ; 
weir  called  nasbah,  199,  200 

Feeder  canal  of  basins,  19,  20,  21 

Feeder  sluices  of  basins,  1 7 

Felix  Jones,  Commander,  on  Mesopo 
tamia,  5 

Ferro-concrete,  141 

Filling  and  emptying  locks,  263 

Filter  bed,  Beresford's,  124,  125,  132 

Financial  prospects  of  irrigation  scheme, 
250,  256 

Flood.     See  also  Inundation 

Flood  canals,  design  of,  20,  21  ;  gradients, 
25  ;  in  India,  not  inundation,  26 

Flood,  crops  after,  Egypt,  3  ;  discharge 
of  canals,  Egypt,  178  ;  discharges 
from  flow-off  of  catchment,  68  ;  dis- 
tribution, 1 6,  17  ;  earliest  recorded, 
on  Euphrates,  5  ;  embankments,  237— 
243  ;  extreme  low,  21  ;  gradient.  68  ; 


294 


INDEX. 


inundation  by,  13,  14  ;  irrigation,  26  ; 
level,  mean,  20,  21  ;  levels,  rise  of, 
238  ;  levels  in  delta  of  Egypt,  238  ; 
marks,  68 

Flood  of  Thapangaing  river,  206 ;  period 
of  emptying  basins,  19,  22  ;  period  of 
filling  basins,  19,  20,  22 

Flood  rivers,  characteristics  of,  12  ;  the 
Euphrates,  3  ;  the  Nile,  3  ;  the  Pun- 
jab, India,  25 

Flood  rotations,  183,  184,  185 

Flood  season,  crops,  25  ;  Egypt,  3,  38 ; 
Mesopotamia,  3 

Flood  spill  channels,  238  :  surface  slope, 
68  ;  system  of  inundation,  28  ;  water 
for  fertilisation,  255 

Floods,  comparison,  Egypt  and  Meso- 
potamia, 3  ;  Egypt,  12  ;  Mesopotamia 
\2 ;  of  the  Euphrates,  3,  12  ;  of  the 
Indus,  12  ;  of  the  Nile,  12  ;  of  the 
Tig"5.  3i  12 ;  Sind,  India,  12  ;  un- 
flooded  areas  in,  1 8 

Floor.  Assiout  barrage,  142  :  Zifta  bar- 
rage, 142 

Floors,  ashlar  covering  of,  116,  141,  142  ; 
below  falls,  195,  196  ;  of  head  sluices, 
192  ;  of  homogeneous  material,  142  ; 
of  regulating  works,  192 

Flow  irrigation.     See  Free-flow 

Flow-off  and  re.-ervoir  capacity,  70  ; 
catchment,  59,  67,  68  ;  of  rainfall,  64, 
65,  66  ;  statistics,  65,  66 

Flow  period  of  basin  feeders,  2O,  21  ;  or 
base  of  "duty,"  40 

Flumes,  207 

Flush  irrigation.     See  Free-flow 

Forces  acting  on  weirs,  116 

Formulas  of  catchment  discharge,  69  ; 
irrigation,  269 — 277 

P'oundation  borings,  74  ;  springs,  143 — 
150,  166 ;  wells,  123  :  wells  of  Nadrai 
aqueduct,  154 

Foundations  by  cement  grout,  157 — 163, 
166,  167  ;  by  compressed  air,  153;  by 
well-sinking,  153,  154  ;  got  in  by 
pumping,  143, 145,  149,  150  ;  methods 
of  getting  in,  142—170;  of  dams,  59, 
7r»  73*  75  :  °f  Delta  barrage  grouted, 
163,  164,  165;  of  syphons.  209,  211 

Fouracres'  shutters,  125 


Foy  Sagar  Tank  dam,  77,  80 

France,  canal  management,  232  ;  curved 
dam,  92  ;  Furens  dam,  82  ;  Gros  Bois 
dam,  102  ;  Government  supervision, 
235  ;  inland  waterways,  259  ;  intervals 
between  waterings,  39  ;  irrigation  in, 
10 ;  land  values,  10  ;  navigable  water- 
ways, 235 

Fiance,  North  of,  rainfall,  I  ;  rotations, 
215  ;  South  of,  "  duty  "  of  water,  39  ; 
Verdon  dam,  102  ;  water  rates,  227 

French  type  oi  river  regulator,  107,  112 

Freeflow  drainage,  255;  irrigation,  25, 
182,  183,  255 

Free-fall  weirs,  199 

Fuel  for  pumping,  256,  257 

Full  supply  level,  184 

Furens  dam,  82,  87,  88,  91 

"  Furrows,"  South  Africa,  27 


G. 

GATE  recess  of  locks,  202,  264 

Gates  of  barrages,  Egypt,  127  ;  of  Delta 
barrage,  137;  of  Kosheshah  escape, 
194,  195  ;  of  locks,  262,  263  ;  of 
undersluices,  125,  126  ;  of  wood,  202  ; 
of  wrought  iron,  201,  202  ;  Reinold's, 
101,  102  ;  Stoney's,  126,  127,  134, 
202  ;  with  rollers,  201,  202 

Ganges  canal  distributaries,  180,  181  ; 
drainage,  186  ;  loss  of  water  in,  35  ; 
Lower,  and  Nadrai  aqueduct,  67  ; 
Rutmoo  crossing,  207  ;  weirs,  86 

Ganges,  training  of  river,  246 

Garda,  Lake,  46 

Gauge,  uniformity  of,  259 

Geneva,  Lake,  46 

Genii  river,  source  of  Granada  supply, 
109  ;  water-wheels,  106 

Germany,  inland  waterways,  259 

Ghats,  India,  58,  60 

Giza  pumping  station,  Kgypt,  138 

Godaveri  canal  system,  258  ;  weir,  114 

Gordon,  Mr.  W.  B.,  on  Cape  Colony, 
26,  27 

Government  control  of  irrigation,  228, 
232  ;  Departments  of  Irrigation,  229, 
230 ;  duty  regarding  storage  works, 
58  ;  duty  regarding  water  supply,  235; 


INDEX 


295 


engineers,  duties  of,  228,  229  ;  respon- 
sibility, 236  ;  supervision  of  waterways, 

235 

Gradient  hydraulic,  117,  120,  121;  of 
canals,  173,  177  ;  of  drains,  189  ;  of 
flood  in  flow-off  streams,  68 

Gradients  of  flood  canals,  25 

Grading  of  canals,  no,  III 

Granada,  irrigation,  109  ;  Moors  first 
engineers  of,  IO ;  water  rates,  228 

Grand  anicut  of  Madras,  29,  ill 

Great  lakes  of  St.  Lawrence  basin,  33 

Gros  Bois  dam,  102 

Gross  area  of  crop,  Egypt,  37,  178 

Grouted  area  of  lock  foundation,  162 

Grouted  blocks,  dimensions  of,  161 

Grouting  apparatus  for  blocks,  158,  159; 
apparatus  for  piles,  152,  156;  founda- 
tions of  Delta  barrage,  163,  164,  165  ; 
to  get  in  ends  of  pipe  syphon,  168, 
169  ;  joints,  Detroit  tunnel,  170  ; 
pitching,  121  ;  lock  foundations,  161 
— 163  ;  well  interval  pipes,  156,  157 

Groynes  for  river  training,  246 

Guadalquivir  river,  39,  172 

Guiding  spurs  above  weirs,  Il6,  119; 
below  escapes,  197 

Gwynne  centniugal  pumps,  139,  257 

H. 
HAMMURABI  and  irrigation  in  Chaldea, 

4,  7,  28,  29 
Harbours,  basins  as  lock  chambers  in, 

261 

Hasisatm,  Chaldean  Noah,  5 
Heading  up  by  river  regulator,  no,  in 
Head  of  canal,  "  duty"  at,  41 
Head  on  Delta  barrage,  130,   131  ;  on 

Kosheshah     escape,     194.:     on     Zifta 

barrage,  133 

Head  reach  of  canal,  1 10,  1 1 1 
Head  sluice  floor,  192  ;  of  basin  feeder, 

21,  22,  23  ;  of  branch  canals,  192  ;  of 

main  canal,  174,  190,  191,  192  ;  vents, 

191 

Head  works  of  Granada  canals,  109 
Henares  canal,  water  rates,  228 ;  weir, 

Spain,  85,  86 
Hermitage  breakwater,  Jersey,  grouting, 

164 


Herodotus  and  Lake  Moeris,  29,  47  ;  and 
Mesopotamia,  4 

High  Line  canal  bench  flume,  207 

Higham,  Sir  T.,  on  Indian  Irrigation, 
58  ;  on  Marikanave  reservoir,  90,  91 

Himalayas,  rainfall,  2 

Holland,  windmills,  105  ;  land  reclama- 
tion, 253 

Horizontal  closure  of  vents,  200,  2OI 

Horse  power,  Divi  pumps,  139;  of 
pumps,  Komombos,  139  ;  of  pumps, 
Lower  Egypt,  139  ;  pumping,  138,  139 

Humid  conditions,  U.S.A.,  2;  region, 
rainfall,  46 ;  region  traversed  by  St. 
Lawrence  river,  46 

Humidity  affecting  evaporation,  35 

Hydraulic  formulas,  269 — 277  ;  gradient, 
117,  120,  121  ;  power,  Assuan  lock, 
263 

I. 

IBRAHIMIA  canal  syphon,  168 
Idaho  canal,  Camere  curtain,  202 
Impermeable  apron,  130 
Impermeable  floor,  132 
Impermeable  platform,  121,  130 
Inclines  on  navigation  canals,  262 
India,  aqueducts,  204,  205  ;   areas  irri- 
gated, 8,  62  ;   area  under  wells,  43  : 
Betwa  dam,  84  ;    Bhatgarh  dam,  95. 
96,    100,    102 :    capacity  of  reservoir, 
33  ;  capital  expenditure,  8 ;  Coleroon 
anicut,    135  ;    crops,    37  ;    dam    and 
storage,   59  ;    development,  63  ;    Divi 
pumping    scheme,   257  ;    "  duty "    of 
water,   32,   33,    36—39,    41  ;    earthen 
dams,    72 ;    flood    canals,    26 ;    flood 
crops,  25  ;   flow-off,  65,  66  ;  form  of 
spurs,   243 ;   formation  of  deltas,  13  ; 
foundations    by     well-sinking,     153  ; 
Ganges   and   Bari   Doab   canals,    35 ; 
Ganges  canal  weirs,  86  ;   Government 
controls    irrigation,    228  :    history    of 
irrigation  of,  7 ;  increase  due  to  irri- 
gation in,  8  ;  ir*»ndation  canals,    18  ; 
inundation     in,    25,    26:     Irrigation 
Department,    229;    main  canal  cross- 
section,    179  ;    Marikanave   dam,   89, 
90,    102,    103 ;  Nadrai   aqueduct,    67, 
68 ;  navigable  canals,  259  ;   navigable 


296 


INDEX. 


waterways,  258 ;  needle  closure,  200  ; 
Nira  dam  or  weir,  87,  88;  Penner 
river  regulator,  126,  134  ;  Periyar 
dam,  88.  89  ;  profit  on  expenditure,  8  : 
pumping  for  irrigation,  139  ;  rainfall. 
I  ;  reservoir  escapes,  69,  70  ;  restric- 
tion of  cropped  area,  222,  223;  results 
of  irrigation,  8;  rice  crop,  38;  rich  in 
population,  256;  river  banks,  237, 
240;  riverv  of  Upper,  snow-fed,  45  : 
rotations,  216,  217  ;  silting  up  of 
reservoirs,  92,  95,  96  ;  Sone  anicut, 
113;  storage  reservoirs,  58;  syphons, 
209,  210;  tank  irrigation,  6l,  62; 
tanks,  104;  the  Idt  or  picottah  of, 
104 ;  the  mote  of,  104 ;  three  river 
project,  61  ;  training  works,  246 : 
value  of  crops,  8  ;  watering  periods. 
38  ;  water  rates,  226  ;  waterways 
public,  235  ;  years  of  drought,  8 

Indian  Irrigation  Commission,  58 ;  type 
of  river  regulator,  107,  112,  114;  weir 
of  the  future,  134  ;  weirs,  crest  shutters 
of,  125 

Indus  river,  12,  25,  45 

Infiltration,  180,  182,  183 

Inflow  of  lakes,  32 

Inflow  of  reservoirs,  48 
nland  waterways,  259 

Inlet  regulator,  22 

Inlets  for  drainage,  203 

Inlets  of  lock  sluices,  264 

Insubmergible  dams,  83 

Intervals  between  foundation  wells,  154, 

155,  156 

Intervals  between  witerings,  34,  36 — 39 

Inundation  areas,  26  ;  by  flood,  13,  14  ; 
canals,  14,  15,  138  ;  canals,  gradients 
of,  25  ;  canals,  India,  25,  26  ;  canals, 
silt  in,  1 8,  19  ;  control  of,  by  Egyp- 
tians, 3  ;  in  India,  25,  26  ;  India  and 
Egypt  compared,  25,  26;  irrigation, 
Egypt,  3 ;  irrigation,  Mesopotamia,  3 ; 
natural,  3  ;  of  basins,  depth  of,  20,  22  : 
protection  from,  28. 

Inundation.     See  also  Flood 

Iron  aqueducts,  207 

Iron  sluice  gates,  201 

Irrigable  area,  212 

Italian  "  duty  "  of  water,  38 


Italy,  distribution  of  water,  222 ;  Irrigation 
Association,  West  of  the  Sesia,  222, 
230;  irrigation  in,  10 ;  land  reclama- 
tion, 253  :  modules,  214  ;  Po  embank- 
ments, 240  ;  rotation  periods,  214, 
215  ;  watercourses  public,  235  ;  water 
rates,  227 

J- 

JAVA,    irrigation    administration,    230  ; 

land  tax,  226  ;  rotation  system,  216, 

223—225  ;  water  rates,  226 
Jhelum  river,  61 


K. 

KAIR  tank  dam,  77,  78 
Kali   Nadi  aqueduct.     See  Nadrai  aque- 
duct ;  discharge,  67 
Kassassin  pumping  station,  257 
Kennedy's  velocity  formula,  175,  176 
Khamis  undersluice,  Algeria,  93 
Kharif  crops,  25,  26,  37  ;  "  duty,'1  India, 

39  ;  season,  37 

Khartoum,  Nile  above,  52,  53 
Khatatbeh  pumping  station,  135,  136 
Kistna  river,  pumping  from,  257  ;  weir, 

in,  114 

Komombos  plain,  138,  139 
Kosheshah  escape,  194,  195 
Kurun  Lake,  Egypt,  2? 


LADO  on  Upper  Nile,  53 

La  Grange  dam,  83,  84 

Lake  Albert,  46,  54,  55,  56,  57  ;  Albert 
Edward,  46  ;  Baikal,  46  ;  Como,  46  ; 
Constance,  46  ;  discharges,  32  ;  Garda, 
46  ;  Geneva,  46  ;  inflow  and  outflow, 
32 ;  Kurun,  29 ;  levels,  32,  45  ; 
Maggiore,  46  ;  Mareotis,  256  ;  Moeris, 
29. 30,  47,  52  ;  Neuchatel,  46  ;  Nyassa, 
46 ;  source  of  supply,  32 ;  sources  of 
rivers,  45,  46  ;  Tanganyika,  46 ; 
Tsana,  2  ;  Victoria,  46 ;  Whiting,  97 

Lakes,  Africa,  at  White  Nile  sources,  46, 
52,  54  ;  at  river  sources,  45,  46 ; 
natural  reservoirs,  48  ;  of  St.  Lawrence 
basin,  33,  45,  46 ;  on  Mississippi,  47  ; 
Russia,  47 


INDEX. 


297 


Land,  configuration  of,  31 ;  bordering 
Mediterranean,  level  of,  29 ;  reclama- 
tion, 253—256 ;  surface,  raising  of, 
237,  238  5  surface  slope,  260  ;  surface 
slope  of  basins,  19,  20;  tax,  Egypt, 
226  ;  tax,  Java,  226 

Land  values,  basin  and  perennial  irriga- 
tion, 28  ;  Castellon,  Spain,  11  ;  Egypt, 
7;  France,  10 ;  Madrid,  II  ;  Murcia, 
Spain,  ii  ;  Spain,  II  ;  Transvaal,  9, 
10  ;  United  States,  9 

Laramie  river,  60 

Lat  of  India,  104 

Leaf  gate  of  locks,  262,  263 

Level  crossing  escape,  22 

Level  crossings  for  drainage,  203,  204, 
206,  207 

Level,  mean  flood,  20,  21 

Levees,  America,  240 

Levels,  fluctuation  of  lake,  45 

Levels  of  lake  observations,  32 

Levels  of  river  affected  by  rainfall,  45 

Lift  drainage,  255 

Lift,  Divi  pumps,  140,  257 

Lift  irrigation,  182,  183,  255 

Lift,  Komombos,  139 

Lift  of  locks,  265 

Lift  of  pumps,  Upper  Egypt,  138 

Lifting  apparatus,  43 

Lifting  water,  cost  of,  139,  140 

Lifts  on  navigation  canals,  262 

Limitation  of  water  supply,  252 

Line  for  irrigation  canal,  258  ;  navigation 
canal,  258 

Lock  chambers,  261  ;  chamber  walls, 
264,  265  ;  dimensions,  262  ;  founda- 
tions grouted,  161 — 163;  sites,  260; 
sluice  inlets,  264  ;  sluice  outlets,  263, 
264  ;  Zifta  barrage,  264,  265  ;  gates 
and  sluices,  261 — 264 

Locks  and  silt  deposit,  264  ;  Assuan 
dam,  262,  263,  266 ;  cracks  during 
construction,  266  ;  double,  265  ;  filling 
and  emptying,  263  :  ladder  of,  265  ; 
lift  of,  265  ;  on  navigable  canals,  195  ; 
settlement,  266  ;  uniform  gauge,  259 

Lombardy  and  irrigation,  10 

Loose  rock  dams,  71,  79,  80 

I.orca,  Moors  first  engineers  of,  IO 

Lorca  water  rates,  228 


Loss  by  evaporation  and  absorption,  31, 
35.  48,  5°>  52—57>  70,  71,  216 

Loss  of  water  in  transit,  36,  63 

Lower  Egypt  irrigation,  129,  135  ;  Nile 
banks,  239,  240 ;  pumps,  139 ;  silt 
deposit,  177  ;  we' Is,  44 

Low-lying  lands,  253,  255 

Low  supply,  Nile,  37 

M. 
MADRAS,  Cauvery  weir,  29  ;  consolidated 

rate,  227  ;  Divi  pumping  project,  257  ; 

Godaveri  canals,  258  ;  Grand  anicut, 

29,      in;      Province,      rainfall,      2; 

pumping,    139  ;  Ryves'  formula  used, 

69  ;  tank  system,  61,62;  land  values, 

II 
Madura  irrigated  from  Periyar  catchment, 

60 

Maggiore.  Lake,  46 
Mahanadi  weir,  114,  116 
Mahmudia  canal,  137 
Main  canal  discharges,  185  ;    irrigation, 

179 
Main   canals,  alignment  of,   171  ;  water 

surface,  179,  180 
Main  drains,  187,  188,  189 
Maladevi  tank  dam,  73,  75 
Malaga  water  rates,  228 
Mareotis  Lake,  256 
Marikanave  dam,  89,  90,  102,  103 
Marikanave  reservoir,  89,  90,  91 
Marshes,  Nile,  channel  through,  55,  56, 

57 

Marshes  on  Nile,  47,  52—57 
Masonry  cores,  75,  76  ;  dams,  71,  72,  78. 

80  ;  works  classified,  190 
Mataana  pumping  station,  138 
Material  of  lock  gates,  262  ;  of  spurs  and 

revetments,  243,  248 
Materials  of  construction,  141 
Mattresses  for  river  training,  249 
Mead,  Mr.  Elwood,  on  control  of  irriga- 
tion, 233,  234  ;  on  history  of  irrigation, 
U.S.A.,  29;  on  irrigation  in    U.S.A., 

8,9 

Measure  of  "  duty  "  of  water,   32;  units 

of,  33,  34 
Mediterranean  and  Nile  branches,   137  ; 

lowlands  bordering,  29 


298 


INDEX. 


Menem  et  Ali,  29,  128 
Mesopotamia,  3,  4,  6,  7,  12,  45 
Meters  for  water  measurement.  213 
Mex  pumping  station,  256 
Mexico,  arid  regions  of,  9 
Midnapore  canal  system,  258 
Miner's  inch,  34 
Mississippi,  47,  248,  249 
Missouri  river  protection,  249 
Modesto  district,  California,  9 
Modules,  213,  214 
Moeris,  Lake,  29,  30,  47,  52 
Montana,  "  duty  "  of  water,  39 
Moors  and  irrigation,  10,  109 
Mote  of  India,  104,  105 
Mougel  and  the  Delta  barrnge,  128 
Msta  river,  Russia,  47 
Multan  district,  25 
Mundaring  dam,  88,  102,  103 
Murcia,  Spain,  land  values,  1 1  ;  Moors 
first  engineers  of,  10 

N. 

NADRAI  aqueduct,  67,  68,  154,  204—206 

Naga  Hamadi  pumping  station,  138 

Nahrwan  Canal,  6 

Narora  weir,   114—122 

Nasbahs  of  Fayum,  199,  200 

Navigable  canals,  175,  195,  259  ;  con- 
ditions, 248  ;  waterways,  258 

Navigation  canal,  258  ;  inland,  47 — 49, 
258 — 266  ;  on  irrigation  canals,  258  ; 
St.  Lawrence  river,  46  ;  suitable 
velocity  for,  259,  260 

Needle  closure,  200 

Neuchatel,  Lake,  46 

New  Croton  dam,  76,  90,  91,  100  —  103 

Newell,  Mr.  F.  H.,  on  "  duty  "  of  water, 
39  ;  on  the  arid  regions,  U.S.A.,  9 

New  Mexico,  ancient  irrigation  works,  30 

New  York,  New  Croton  dam,  76  ; 
Quaker  Bridge  dam,  102  ;  water 
supply,  91 

Neville's  rule  for  distributary  section, 
181,  182 

Nile  above  Khartoum,  52,  53 

Nile,  a  flood  river,  3,  12 ;  and  Lake 
Moeris,  29 ;  Assuan  dam,  28,  96 — 
100  :  banks,  238 — 240;  channel 
through  "  Sudd,"  55,  56,  57  ;  delta, 


rate  of  rise  of,  238  ;  discharge,  50  ; 
effect  of  solid  dam  on,  98  :  Egypt's 
carrier  of  rain  water,  43  ;  lakes,  46  ; 
low  supply,  37  ;  marshes,  swamps,  or 
Sudd,  47,  52—57  ;  regulators,  128  ; 
results  of  efficient  control  of,  6  ;  stor- 
age in  equatorial  lakes,  52,  54,  56,  57  ; 
storage  of  surplus,  49  ;  subsidiary  weirs, 
124 ;  temporary  dams,  137  ;  valley, 
deltaic,  13  :  valley,  inundation  in,  13; 
valley  reservoir,  52 

Nira  canal  superpassage,  209  ;  dam,  86, 
88 

Normandy,  prosperity  due  to  irrigation, 
IO 

Northern  India,  canals  still  possible,  58 

Notch  falls,  196,  198,  199 

Notch  form  for  falls,  198 

Nyassa,  Lake.  46 

O. 

OFF-TAKE  channel  of  ba«n  feeder,  22  ; 
of  main  basin  feeders,  18,  19 

Ogee  fall,  form  of,  85,  86,  195 

Ohio  river,  108 

Okhla  weir,  114,  123 

Opis,  present  aspect,  5 

Orchard  cultivation,  39 

Oris-a  canal  system.  258 

Outflow  of  Albert  Nyanza,  56  ;  lake 
sources,  32  :  Lake  Albert.  55  ;  reser- 
voirs, 48 

Outlet  of  Albert  Nyanza,  57  ;  dams,  76  ; 
earthen  dams,  72 

Outlets  of  lock  sluices,  263,  264 

Outlets,  rotation  by,  217 

Over- watering,  251,  252 

P. 

PARALLEL  distributaries,  180 
Pearson's  theory  of  dam  stresses,  IOO 
Penner  river  regulator,  126,  134 
Percolation  downwards  into  drains,  253, 

255 ;    supply     obtained     from,     137  ; 

under   dams,      74 :     under    barrages, 

132;  under  weirs,  117,   121 
Perennial    irrigation,    Mesopotamia,    4; 

Upper  Egypt,  ^i  38 

Perennial  irrigation  system,  28,  29,  30 
Perennially  irrigated  land,  value  of,  28 


INDEX. 


299 


Period  for  calculating  "duty,"  Egypt, 
42  ;  of  flow,  40 ;  ot  pressure  or 
greatest  demand,  41,  42  ;  of  supply, 
214,  219 

Periods  between  waterings,  34,  36 — 39 

Periyar  dam,  60,  88,  89 

Periyar  river,  60,  61 

Permeable  spurs,  248 

Persian  wheel,  104,  105 

Pharaohs,  records  of,  about  irrigation,  7 

Philse,  submersion  of,  51,  70 

Picottah  of  India,  104 

Piedmont,  plains  of,  10  :  irrigation  con- 
trol, 230,  231  ;  water  charges,  227 

Piles,  as  curtains,  122  :  cast  iron.  151, 
1S2>  *55  5  grouting  joints  of,  152  ; 
rows  of,  130,  132,  133,  147 

Piling.     See  Piles 

Pipe  syphons,  construction  of  ends,  168, 
169 ;  method  of  laying,  167,  168 ; 
without  concrete,  211 

Pipes,  sub-irrigation  from,  39 

Piping,  or  leakage  under  floor,  115,  Il6, 

119,    122,  129 

Po  river,  46 

Po  valley  land  reclamation,  253 

Poiree  dams,  107 

Pooling  below  regulators,  197 

Population,    Dongola,  105  ;    wanted  for 

reclamation,  255 
President  Roosevelt's  Message  to  Con 

gress,  58 
Pressure,  or  greatest  demand,  period,  41. 

42 
Pressures,    Assuan   dam,    99 ;    in  dams, 

IO2,  103;   in   syphons,   208,  209;    on 

weirs,  116 — 118,  120,  121 
Priorities,  United  States,  224,  225 
Products  raised   by  canal,    259;   trans- 
ported by  canal,  259 
Profit  on  expenditure,  India.  8 
Programme  of  emptying  basins,  23,  24  : 

of  filling  basins,  23,  24 
Programmes     of     rotations,     217 — 221, 

223—225 
Project,   based  on  "  duty,"   34  :  canal, 

30 ;   for  a  basin  system,  19  ;  for  Nile 

storage,   49  ;   irrigation,   40 ;    storage, 

59;  three-river,  India,  6l 
Protective    apron,    Assuan    dam,     100  ; 


banks,  14.  237—243;  banks,  action 
of,  13  ;  material  for  banks,  241  ;  revet- 
ments or  pitching  of  banks,  24,  242, 
243  ;  spurs,  242,  243  ;  wall  of  basin 
banks,  24 

Puddle  clay  apron,  119,  120,  122  ;  core, 
75.  76,  78  ;  face  to  dam,  78 ;  trench, 
74,  75 

Pumping,  expenditure,  256,  257 ;  for 
reclamation,  253,  254,  255  ;  India, 
139,  257 

Pumping  station,  Divi,  India,  139; 
horse-power,  138,  139 

Pumping  stations,  105,  106,  129,  135, 
256,  257  ;  Giza,  138  ;  Upp-r  Egypt, 

138 

Pumps,  Atfeh,  137  ;  in  Upper  Egypt, 
138  ;  Komombos,  139;  on  main  drains 
257;  period  of  working,  218,  219,  220 
used  in  irrigation,  106 ;  used  in 
reclamation,  244,  255,  257  ;  worked 
by  electricity,  257 

Punjab,  crops,  37;  inundation  canals, 
25  ;  rainfall,  I 

Q. 

QUAKER  Bridge  dam,  maximum  pres- 
sure, 102 ;  replaced  by  New  Croton 
dam,  91 

Quantity  of  water,  rate  levied  on,  213 
Quantity  of  water  required  for  irrigation^ 
36,  37-  38>  40,  41 


RABI  crops,  India,  25,26,  37;  "duty" 

for,  41  ;  season,  37  ;  sowings,  41 
Rain,  its  effect  on  "duty''  value,  42 
Rain  reaching  Lake  Albert,  56 
Rain  water,  rivers  carriers  of,  43  ;  versus 

well  water,  44 

Rainfall,  Abyssinia,  2 ;  and  reservoir, 
63,  64,  65  ;  capriciousness  of,  31  ; 
catchment  area,  2  ;  Central  Provinces, 
India,  2  ;  deficiency,  31 ;  deficiency, 
India.  8  :  distribution  of,  I,  2  ;  effect 
on  river  levels,  45 :  Egypt,  2.  3  ; 
England,  I  ;  flow-off,  64,  65,  66  ; 
Ghats,  India,  60 ;  Himalayas,  2 ; 
humid  regions,  46  ;  India.  I  ;  lost  by 
evaporation,  47  ;  Madras  Province,  2 ; 


300 


INDEX. 


Mesopotamia,  3 ,  North  of  France,  I  ; 
not  constant,  41  ;  of  arid  regions, 
U.S.A.,  9 ;  of  catchments,  43  ;  of 
region  to  be  irrigated,  31  ;  Periyar 
catchment,  60 ;  primary  source  of  sup- 
ply, 43  ;  Punjab,  India,  I  ;  record,  64, 
68 ;  run-off,  2  ;  Sind,  I  ;  source  of 
irrigation,  2  ;  statistics,  64,  68  ;  Sudan, 
2  ;  U.  S.  America,  2  ;  West  Coast  of 
India,  2  ;  Western  Ghats,  India,  58 

Rain-fed  rivers,  45 

Rainy  region,  Abyssinia,  2  ;  Sudan,  2 

Raising  of  land  surface,  237,  238  ;  of 
river  bed,  237,  238 

Rankine's  rule  for  puddle  cores,  75 

Rapids,  194,  196 

Rates  for  water,  used  in  irrigation,  213, 
226 — 228  ;  America,  227  ;  Egypt,  226  ; 
France,  227  ;  India,  226  ;  Italy,  227  ; 
Java,  226  ;  Spain,  227,  228 

Ravi  river,  61 

Ravi  syphon,  209,  210 

Reach  of  canal  as  lock,  261 

Rechna  Doab  and  Chenab  canal,  7 

Reclamation  by  deep  drains,  253,  255  ; 
by  pumping,  253,  254  ;  by  surface 
washings,  253,  254  ;  by  training  rivers, 
248  ;  of  land,  253—256  ;  use  of  flood 
water  in,  255  ;  want  of  population  for, 
255,256 

Reference  books,  278 — 281 

Regulating  apparatus,  200— 202 

Regulating  falls,  177 

Regulating  works  of  basins,  21 

Regulator,  Egyptian  type,  131,  132  ;  for 
river  reclamation,  248 ;  inlet,  22  ;  on 
navigable  canal,  260,  261  ;  Penner 
river,  126,  134  ;  river,  109,  no,  in 

Regulators,  basin,  design  of,  23  ;  Nile, 
128 ;  of  basins,  15,  16,  17,  21  ;  of 
Lake  Moeris,  48  ;  of  rivers,  107  ;  on 
canals,  193  ;  river,  of  the  future,  134 

Reinold's  gates,  101,  102 

Remission  of  land  tax.  226 

Replenishment  of  reservoir,  64,  67 

Reservoir,  absorption  in,  41  :  Assuan,  41, 
5i>   S2,    56.   97—99,    221  ;   Bhatgarh 
97  ;    by  wash,   67  ;    capacity   of,    33 
dam,    57.    58.    59;    '•  duty  "    at,    41 
Egypt,  49>   5°J  escape,  65,  67,  69 


evaporation  in,  41,  50;  features  of 
59  ;  filling  of,  63  ;  in  Nile  valley,  52  ; 
Lake  Moeris,  29,  48  ;  Lake  Tsana,  2  ; 
Marikanave,  89,  90,  91  ;  Periyar,  60  ; 
project,  67,  68;  replenishment,  64,67  ; 
site.  59,  63,  64,  70  ;  site  for  E^ypt,  50  ; 
source  of  supply,  48  ;  storage  capacity, 
50,  70  ;  study,  68  ;  study  by  Willcocks 
in  Egypt,  50  ;  supply  from,  48  ;  waste 
weirs,  69  ;  water  "  duty, ' '  40 

Reservoirs,  artificial,  47,  48.  57,  58  ; 
conditions  favouring,  63  ;  demand  for, 
63  ;  for  storage,  India,  58  ;  Govern- 
ment work,  236  ;  inflow  and  outflow. 
48  ;  natural,  lakes  as,  45 — 48  ;  natural, 
snowfields  as,  45  ;  river- fed,  62  ;  Rus- 
sia, 47  ;  South  Africa,  59  ;  silt  deposit 
in,  92.  95,  96,  98  ;  source  of  supply, 
104  ;  United  States,  58 

Results  of  Assuan  dam,  28  ;  of  efficient 
control  of  Nile.  6  ;  of  irrigation,  4,  1 1 ; 
of  irrigation  in  France,  10  ;  of  irriga- 
tion in  India,  8  ;  of  irrigation  in  Spain, 
n  ;  of  neglect  of  irrigation,  n 

Retirement  of  river  banks,  242,  243,  248 

Reverse  lock  gates,  263 

Revetments  for  bank  protection,  242. 
243 

Revetted  slopes  of  regulating  works, 
192 

Reynolds,  Mr.  B.  P.,  on  weirs,  134 

Rhine,  moderated  by  lakes,  46;  river 
banks,  240 

Rhone,  moderated  by  lakes,  46 

Rice  crop,  Egypt,  37  ;  India,  38 

Rice, ''duty,"  38 

Rice  irrigation,  220,  221,  223—225 

Rice,  Italy,  38 

Rice,  water  allowance,  222,  223 

Rio  Grande,  ancient  irrigation  on,  30 

River  Cauvery  weir,  29  ;  Chenab,  61  ; 
Congo,  46  ;  Darro,  109  ;  Detroit 
tunnel,  169,  170:  Genii,  109;  Genii 
and  waterwheels,  106 ;  Guadalquivir, 
39,  172 ;  Jhelum,  61  ;  Laramie,  60  ; 
Mississippi,  47  ;  Msta,  47  ;  Ohio,  108  ; 
Penner  regulator,  126,  134;  Periyar, 
60,  6 1  ;  Po,  46  ;  Ravi,  61  ;  Rhine,  46 ; 
Rhone,  46  ;  Shire,  46  ;  Sobat,  55  :  St. 
Lawrence,  46 ;  Thapangaing,  206 ; 


INDEX. 


301 


Vaigai,  60,  61  ;  Volga,  47  ;  Yenisei,  46  ; 
Zak,  South  Africa,  26  ;  Zambezi,  46 

River  banks,  24,  25,  237 — 243  ;  bed, 
raising  of,  237,  238  ;  bed  reclamation, 
248  ;  capacity,  238  ;  dams,  106,  107 ; 
delta,  growth  by  deposit,  12  ;  discharges 
31  ;  encroachments,  243  ;  gauges, 
31  ;  levels,  effect  of  rainfall  on,  45  ; 
natural  discharge,  49  ;  regulators,  107, 
109,  no,  in  ;  regulators  of  the  future, 
134;  spurs,  247,  248  ;  training  works, 
245-249;  velocity,  173,  174,  175; 
weir  alignment,  114;  weir,  South 
Africa.  26 

River-fed  reservoirs,  62 

Rivers,  carriers  of  rain  water,  43  ;  fed 
by  rain,  45  ;  fed  by  snow,  45 ;  in 
flood,  12  ;  Nature's  waterways,  43  ;  of 
flood,  characteristics  of,  12  ;  of  flood, 
the  Euphrates,  12  ;  of  flood,  the  Indus, 
12  ;  of  flood,  the  Nile,  12  ;  of  flood, 
the  Tigris,  12;  offtake  of  basin  feeders 
from,  1 8,  19 ;  principal  source  of 
supply,  45  ;  source  of  supply,  31  ; 
with  lake  sources,  45,  46 

Rockfill  dams,  71,  79,  80;  weir,  109 

Rocky  Mountains,  Colorado,  flow- off 
diversion  through  watershed,  59 

Roosevelt,  President,  Message  to  Con- 
gress, 58 

Rosetta  branch  of  Nile,  135,  137  ; 
barrage,  128  ;  weir,  131 

Ross,  Col.  J.  C.,  on  canal  off- takes,  19 

Rotations,  Egypt,  216,  218 — 222 ;  France, 
215  ;  Italy,  214,  215  ;  Java,  216,  223 
—225 ;  Spain,  215  ;  advantages  of, 
216,  217  ;  by  distributaries,  217  ;  by 
outlets,  217  ;  during  flood,  183,  184, 
185  ;  programmes  of,  217 — 221,  223 — 
225  ;  system,  180,  183,  184,  214—225 

Run -off  of  rainfall,  2 

Run-off.     See  also  Flow-oft 

Russia,  reservoirs  serving  navigable 
rivers,  47 

Rutmoo  torrent  level  crossing,  207 

Ryves*  formula,  69 


"  SAAI  "  dams,  South  Africa,  27 


South  Africa,  development  and  storage, 
236 

Sakia,  104,  105 

Salt  efflorescence,  182 

Salt  lands,  253 

Salt  washings,  183 

Salvador,  M.,  on  cost,  of  preparing  land, 
250 

San  Uiego  flume,  207 

San  Joaquin  drainage,  186 

Scott- MoncriefF,  Sir  C.,  and  Egypt,  136  : 
on  control  of  irrigation,  Italy,  230, 
231  ;  on  distribution,  222 ;  on  land 
values,  France,  10 ;  on  Southern 
Europe,  39  ;  on  well  irrigation,  44 

Scour  of  canal  bed,  175 

Scouring  below  weirs,  115  ;  by  lock 
sluices,  264  ;  sluices,  107,  113  ;  sluices 
of  dams,  92 — 96  ;  undersluices,  174 

Season,  irrigation,  215,  224 

Season,  irrigation  of,  rate  assessed  on, 
213 

Seasons  of  greatest  discharge,  177,  178 

"Second-foot,"  33 

Settlement  of  locks,  266 

Shadouf,  104,  105 

Sheet- piling,  150 

Shubra  well  intervals,  156,  157 

Shutters,  Boule,  107,  108 ;  crest,  112, 
113,  123,  125;  of  undersluices,  125; 
Smart's,  126;  Stoney's,  126,  127,  134, 
202  ;  working  of,  to  exclude  silt,  174 

Sill  on  floor  of  falls,  195. 

Silt.     See  also  Deposit 

Silt  deposit,  24,  25,  I73~i77,2i7;  above 
anicuts,  112,  113,  114;  locks,  264; 
staunching  action  of,  35 

Silt  disposition,  237,  248 

Silt,  deposits  in  canals,  193  ;  exclusion 
through  design  of  head  sluice,  190, 
191  ;  in  floods,  183  ;  inundation  canals, 
1 8,  19  ;  observations  on  Sirhind  canal, 
176  ;  reservoirs,  92,  95,  96,  98 

Silting  of  basin  feeder,  21 

Sind  canals,  58  ;  needle  closure,  200 

Sind,  inundation  canals,  25,  26  ;  irrigated 
by  flood,  12  ;  rainfall,  I ;  water  rates, 
227 

Sirhind  canal,  silt  observations,  176 

Site  of  reservoir  and  dam,  59,  63,  64,  70 


302 


INDEX. 


Site  of  river  regulator,  109,  no,  113 

Sites  of  falls,  260 

Sites  of  locks,  260 

Sky  line  ditch,  60 

Slope  of  land  surface,  19,  20,  173,  177  ; 

water  surface,  19,  20,  21,  173,  177 
Sluice  capacity  of  locks,  262,  263  ;  inlets 

in  locks,   264  ;   outlets  in  locks,   263, 

264 
Sluices,  lock  gates,  263,  264  ;  lock  walls, 

263,  264  ;  of  basins,  21  :  of  locks,  261  ; 

scouring,  of  dams,  92—96 
"  Sluit  "  channels,  South  Africa,  26 
Smart's  shutters,  126 
Snow-fed  rivers,  45,  6 1 
Snowfields,  Nature's  reservoirs,  45 
Solani  aqueduct,  204 
Sone    aqueduct,     113;     canal    distribu- 
taries,   181  ;    \\eir,     114,    123,    125; 

well-sinking  for  foundations  of  weir, 

154 
Source  of  supply,  primary,  rainfall,  43  ; 

principal    rivers,    45 ;    reservoir,    48  ; 

springs  and  percolation,  137 
Sources  of  rivers,  lakes,  45,  46 
Sources  of  supply,  various,  31,  32,  51, 

57,  i°4 

Sowing  of  basin  crop,  24 
Sowings,  rabi,  India,  41 
South  Africa,  development  depends  on 

storage,  59, 63  ;  irrigation  of  flat  lands, 

26,27 
Southern    Europe,    "  duty  "  of    water, 

33 

Spain,  Alicante  dam,  92,  102 ; 
Almanza  dam,  IO2  ;  Andalucia,  172  ; 
dams,  II,  82;  form  of  spurs,  243: 
Henares  weir,  86,  87 ;  irrigation,  10, 
109;  irrigation  administration,  231  ; 
irrigation  concessions,  231,  232  ;  irri- 
gating seasons,  40 ;  results  of  irriga- 
tion, 1 1  ;  rotations,  215,  216 ;  silting  up 
of  reservoirs,  92  ;  Val  de  Infierno  dam, 
92,  98 ;  water  rates,  227,  228  ;  water- 
courses, public,  235  ;  waterwheels,  106 

Spanish  "duty"  of  water,  39;  under- 
sluices,  93,  94,  95 

Spill  channels,  flood,  238 

Spring  levels,  raising  of,  223 

Springs,  as  source  of  supply,  43  ;  closed 


by  cement  grout,  150  ;  in  foundations, 
143 — 150,  1 66;  of  river  bed,  137 

Spurs,  for  canal  protection,  242,  243 ; 
for  river  training,  247,  248  :  guiding, 
Il6,  119  ;  to  stop  pooling.  197 

Stability,  Assuan  dam,  99 ;  of  curved 
dams,  91  ;  of  dams,  81 

State  control  of  irrigation,  Wyoming,  234 

Steel  plate  core,  79 

Steel  tube  syphons,  211 

St.  Lawrence  basin,  33  ;  lakes,  45,  46 ; 
river,  46 

Stouey's  shutters,  126,  127,  134,202 

Storage,  46,  47,  48 

Storage  by  snowfields,  45 

Storage  capacity  of  Albert  Nyanza,  56  ; 
of  reservoir,  33,  70 ;  of  St.  Lawrence 
lakes,  46 

Storage,  Lake  Albert,  57  :  Nile  lakes, 
52,  54,  57  ;  of  Assuan  reservoir,  51  , 
of  Lake  Moeris,  47  ;  of  Nile  surplus, 
49  ;  Periyar,  60  ;  required,  40,  41  ; 
requirements  of  Egypt,  55,  56 

Storage  reservoir.    See  Reservoir 

Storage  reservoirs,  conditions  favouring, 
63  ;  demand  for,  63  ;  India,  58 

Storage,  South  Africa,  59,  236  ;  to  sup- 
plement natural  discharges,  49  ;  United 
States,  58 

Strange.  Mr.  W.  L.,  on  earthen  dams 
72  ;  on  flow-off,  65,  66 

Stresses  in  dams,  81 

Sub-irrigation  from  pipes,  39 

Submergible  dams,  83 

Subsidiary  drains,  187,  188,  189 

Subsidiary  weirs,  83,  84.  131,  133 

Subsidiary  weirs  of  Egypt,  124,  157,  158 

159 

Subsoil  drainage,  253,  254,  255 

Sudan,  as  affected  by  lakes,  46  ;  Dongola 
irrigation,  104  ;  Lake  Tsana  as  reser- 
voir for,  2  ;  rainfall,  2 

Sudd  region,  Nile,  47,  52 — 57 

Sugar  factories,  138 

Summer  rotations,  184,  185 

Summer  season  irrigation,  Egypt,  38 ; 
Spain,  40 

Summers,  low,  Nile,  37 

Super-passages  for  drainage,  203 — 205. 
209 


INDEX. 


303 


Superstructure  of  head  sluices,  192 
Supply,  accommodation  to  demand,  64 
Supply  and  demand,  67,  212 — 214  ;  by 
pumping,  135,  136  ;  from  percolation^ 
137  ;  from  reservoir,  48  ;  New  York. 
91  ;  navigation  canals,  262 ;  of  water 
from  various  sources,  43,  51,  57,  104  ; 
of  water  to  basins,  16,  17;  period 
during  rotations,  214,  219 ;  primary 
source  of,  rainfall,  43  ;  river  source  of. 
31  ;  livers,  principal  source  of,  45 ; 
source  of  reservoir,  48  ;  underground, 

43 

Surface  irrigation,  39 

Surface  washings,  253.  254 

Sutlej  river,  25 

Sweetwater  dam,  92 

Syndicate  of  Valencia,  231 

Syndicates  of  irrigators,  232 

Syphon  aqueduct,  208 ;  canal,  basin 
system,  16,  18  ;  Ibrahimia  canal,  168  ; 
laying  under  running  canal,  167,  168  ; 
masonry,  design  of,  208 — 211;  pressure 
due  to  head,  208,  209  ;  under  basin- 
feeder,  21,  22  ;  under  Ravi  river,  6l 

Syphons  bent,  210,  211  ;  blowing  up, 
208  ;  for  drainage,  203,  204,  208 — 21 1 ; 
horizontal,  210,  211  ;  of  steel  tubes, 
21 1 ;  of  wood,  207  ;  pipe,  construction 
of  ends,  168,  169;  pipe,  method  of 
laying,  167,  168  ;  waterway,  210 


T. 

TALUS  of  Assuan  dam,  100 ;  of  escapes, 

197 ;    of   regulating    works,    192  ;    of 

weirs,  115 

Tanganyika  Lake,  46 
Tanks,  India,  61,  62  ;  source  of  supply, 

104 ;  United  States,   62  ;  waste  weirs 

of,  69,  70 

Tatils,  or  rotations,  India,  216 
Temperature   affecting   evaporation,   31, 

35 

Thapangaing  aqueduct  and  river,  206 
Theory  of  dam  construction,  81 
Thomas  and  Watt  on  river  training,  249 
Tie-back  of  spurs,  244 

Tig"S,  3>  5»  6»  I2>  45 
Titicus  dam,  91 


Traffic,  size  of  lock  to  suit,  262 

Training  rivers,  245 — 249 

Transport  for  produce,  256  ;  of  goods  by 

canal,  259 

Transvaal,  land  values,  9,  10 
Trebeni  canal  head  sluice,  190,  191 
Trial  pits,  74 
Tribunal  of  waters,  231 
Tunnel  under  Detroit  river,  169,  170 
Tunnels,  60 
Turlock  dam,  84,  85 
Turlock  district,  California,  9 

U. 

UNDERGROUND  supply,  43 
Undermining  of  banks,  242,  243 
Undersluice.     See  also  Scouring  sluice. 
Undersluice  shutters,  125 
Undersluices,  Assuan  dam,  98— 100  ;  of 

weirs,  107,  113 

United  Provinces,  India,  crops,  37 
U.S.A.,    aqueducts,  207  :    area  of  arid 

regions,   9 ;    dams   and    storage,   59 ; 

irrigation  in  the,  8,  9  ;  land  values,  9  ; 

levees,  240;  Newell  on  arid  regions, 

9 ;  priorities,  224,  225  ;  rainfall,  2,  9 ; 

storage  reservoirs,  58  ;  tanks,  62,  104 ; 

water  value,  9 ;  West,  drainage,  186 ; 

West,  miner's  inch,  34 
Units  of  measure  of  "duty,"  32,  33,  34 
Upper  Egypt,  and  pumping,  138  ;  basin 

programme,    23,   24 ;    barrage,    132  ; 

inundation  in,  13  :    Komombos,    138, 

139  ;  wells,  44 

Upper  Nile  above  Khartoum,  52,  53 
Upper  Otay  dam,  92 
Urgel  canal  water  rates,  228 
Utah,  "duty"  of  water,  39 

V. 

VAIGAI  river,  60.  6 1 

Val  de  Infierno  dam,  92,  98 

Valencia,  irrigation  syndicate,  231  \ 
irrigation  works  of,  10 ;  Moors  first 
engineers  of,  10  ;  no  water  rates,  228 

Value  of  cotton  crop,  136 

Value  of  crops  compared,  28  ;  India,  8 

Value  of  land,  basin  and  perennial,  28  ; 

Egypt,  7 


304 


INDEX. 


Value  of  time  in  navigation,  262,  263 

Value  of  water,  U.S.A.,  9 

Values  of  land,  Castellon,  II  ;  France, 
IO;  Madrid,  u  ;  Murcia,  ii;  Spain, 
ii  ;  Transvaal,  9,  10  ;  U.S.A.,  9 

Vaucluse,  France,  land  values,  10 

Vegas  of  Spain,  172 

Velocity  of  canals,  216  ;  of  flow  for 
navigation,  259,  260  ;  of  flow  in  canals, 
173—177;  of  flow  in  drains,  189;  of 
river  flow,  173—175  ;  through  syphon, 
210  ;  to  carry  forward  silt,  177 

Vents  of  head  sluices,  191  ;  of  Kosheshah 
escape,  194,  195 

Verdon  dam,  102 

Vertical  closure  of  vents,  200 

Victoria  Nyanza,  46 

Village  watercourses,  loss  in,  35 

"  Vleis  "  of  South  Africa,  26,  27 

Volga  and  navigation,  47 

Volume  of  water  required  for  irrigation,  40 

Vyrnwy  dam,  84,  85,  86 

W. 

WADI  Rayan,  52 
Wales,  Vyrnwy  dam,  84,  85 
Walnut  Grove  dam,  79 
Washing  land,  253,  254,  255 
Waste  weirs,    Bhatgarh  dam,   96,   100, 

101  ;   of  dams,  72,  76,   100,   101  ;  of 

tanks  and  reservoirs,  69,  70 
Water  allowance,  Egypt,  37,  38 
Water  ' '  duty."    See  ' ( Duty  " 
Water  levels,  Delta  barrage,  132 
Water,  loss  of,  31,  35,36 
Water  meters,  213 
Water  rates,  213,  226—228 
Water  rates,  America,  227  ;  Egypt,  226  ; 

France,  227  ;  India,  226  ;  Italy,  227  ; 

Java,  226  ;  Spain,  227,  228 
Water  supply,  31,  43 
Water     supply,     decreed   public,    235 ; 

Egypt,  52,  56  ;  limitation  of,  252 
Water  surface  of  drains,  186 
Water  surface  slope,  canals,    173,  177, 

260  ;  flood  canals,  19,  20,  21 
Water  value,  U.S.A.,  9 
Watercourses,  loss  in,  35 
Water-cushion  below  dams,  83,  84,  85  ; 

below  falls,  195,  196 


Watershed,  the  scientific  boundary,  2 
Watersheds,  59,  60,  64 
Waterspread,  Periyar  reservoir,  60 
Waterwheels,  106 
Watering,  depth  of,  215 
Watering,  excessive,  251,  252 
Watering  periods.  34,  36—39 
Waterings,  intervals  between.  212,    213, 

215,  2l8,  219,   221,  222 

Waterings,  rate  on  number  of,  213 

Waterlogging,  180,  182,  186,  216,  223, 
252 

Watertight  diaphragm  of  dams,  77,  79  ; 
junction  of  iron  and  masonry,  207,  208  ; 
strata,  43 

Waterway  of  drainage  works,  206; 
of  syphons,  210  ;  safety  margin,  192 

Waterways  for  navigation,  258  ;  Govern- 
ment property,  235  ;  inland,  259 

Weeds  in  drains,  189 

Weights  and  measures,  267,  268 

Weir  alignment,  114;  Baiturnee,  114; 
Brahmini,  114;  Burra,  114;  Cauvery 
river,  29  ;  Chenab,  114,  1 1 6,  121,  122  ; 
core- wall  for  foundations,  154; 
Egyptian,  114,  123  —  125,  134;  Goda- 
veri,  114;  Henares,  85,  86;  Indian, 
134;  Kistna,  in,  114;  Mahanadi, 
114,  116;  Narora,  114—122;  Nira, 
87,88;  of  Delta  barrage,  114,  122 — 
125  ;  Okhla,  114,  123 

Weir,  river,  South  Africa,  26  ;  Rosetta 
branch  of  Nile,  131  ;  Sone,  114,  123, 
125 

Weirs,  ckssified,  114;  Delta  barrage, 
use  of  cement  grout,  157—159  ;  forces 
acting  on,  116  ;  free-fall,  199  ;  Ganges 
canal,  86  ;  Indian,  125  ;  parallel  cur- 
rents, 116;  percolation  below,  117; 
piping,  115,  116,  119,  122,  129  ; 
pressures  on,  116 — 118,  120,  121  ; 
scour  below,  115  ;  subsidiary,  83,  84, 
I3l>  I33  J  subsidiary,  Nile,  124 

Well  and  canal  water  compared,  44,  45 

Well  irrigation,  43,  44 

Well  irrigation  area,  India,  62 

Well  sinking  for  foundations,  153,  154 

Well  water  versus  rain  water,  44 

Wells,  area  under  irrigation,  43,  44 

Wells  in  foundations,  123 


INDEX. 


305 


Wells  in  foundations  of  Nadrai  aqueduct, 
154  ;  in  head  of  Ismailia  canal,  155 — 
157,  165,  1 66  ;  irrigation  from,  2  ;  of 
curtain  walls,  120 — 122 ;  source  of 
supply,  43,  44,  104 

West  Coast  of  India,  rainfall,  2 

Western,  Col.  J.  H.,  and  Delta  barrage, 
127 

White  Nile  at  Sobat  river,  55  ;  lakes,  46, 

52,54 

Whiting  Lake,  97 
Willcocks,   Sir  W.,  conclusions  on  silt 

deposit,  176,  177  ;  lecture  on  Chaldea, 

5  ;  on  closing  springs,  147,  148,  149  ; 

on  pumps  in  Egypt,  139  ;  on  pumping 

stations,  257  ;  on  scouring  sluices,  93  ; 

on  South  Africa,  235,  236 ;  reservoir 

study,  50 

Windmills,  105,  106 
Wing  walls  of  aqueducts,  205 
Wings  of  falls,  196,  197 


Wilson,  Mr.  H.  M.,  on  "  duty  '» of  water, 
U.S.A.,  39;  on  safe  pressures  in 
dams,  102 

Wooden  aqueducts,  207 

Wooden  gates,  202 

Wooden  syphons,  207 

Wyoming  code,  233 

\. 

YAKIMA  valley,  Washington,  9 
Yenisei  river,  46 

Z. 

ZAK  river,  South  Africa,  26 

Zambesi  river,  46 

Zifta   barrage,    Egypt,    127,    131—134 

floor,    142 ;    foundations,    145  ;    lock 

264,  265  ;  piles,  151,  155 
Zifta,  head  sluice  above  barrage,  192 
Zola  dam,  92,  93 


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